CN111344606A

CN111344606A - Retroreflective articles including retroreflective elements comprising primary and secondary reflective layers

Info

Publication number: CN111344606A
Application number: CN201880069403.8A
Authority: CN
Inventors: 迈克尔·A·麦科伊; 夏颖; 伍乐民; 什里·尼瓦斯; 斯科特·J·琼斯; 凯文·W·戈特里克; 陈葵
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2017-10-27
Filing date: 2018-10-25
Publication date: 2020-06-26
Also published as: KR20200065062A; WO2019084299A1; US11415731B2; EP3701297A4; EP3701297A1; US20200264351A1; TW201932882A

Abstract

A retroreflective article includes a binder layer including reflective particles and a plurality of retroreflective elements. Each retroreflective element includes transparent microspheres partially embedded in the binder layer. At least some of the retroreflective elements include a primary reflective layer covering portions of the embedded surface area of the transparent microspheres, and a secondary reflective layer provided by portions of the binder layer containing reflective particles adjacent to portions of the embedded surface area of the transparent microspheres not covered by the primary reflective layer.

Description

Retroreflective articles including retroreflective elements comprising primary and secondary reflective layers

Background

Retroreflective materials have been developed for use in a variety of applications. Such materials are often used as high visibility trim materials, for example in garments, to increase the visibility of the wearer. For example, such materials are often added to garments worn by firefighters, rescue personnel, road workers, and the like.

Disclosure of Invention

Broadly, disclosed herein is a retroreflective article that includes a binder layer that includes reflective particles and a plurality of retroreflective elements. Each retroreflective element includes transparent microspheres partially embedded in a binder layer. At least some of the retroreflective elements include a primary reflective layer covering portions of the embedded surface area of the transparent microspheres, and a secondary reflective layer provided by portions of the binder layer containing reflective particles adjacent to portions of the embedded surface area of the transparent microspheres not covered by the primary reflective layer. These and other aspects will be apparent from the detailed description below. In no event, however, should this broad summary be construed as a limitation on the claimable subject matter, whether such subject matter is presented in the claims of the originally filed application or in the claims of a revised application, or otherwise presented during the prosecution.

Drawings

Fig. 1 is a side schematic cross-sectional view of an exemplary retroreflective article.

FIG. 2 is an isolated enlarged perspective view of a single transparent microsphere and an exemplary primary reflective layer.

FIG. 3 is an isolated enlarged side schematic cross-sectional view of a single transparent microsphere and exemplary primary and secondary reflective layers.

FIG. 4 is an isolated enlarged top plan view of a single transparent microsphere and an exemplary primary reflective layer.

Fig. 5 is a side schematic cross-sectional view of another exemplary retroreflective article.

Fig. 6 is a side schematic cross-sectional view of another exemplary retroreflective article.

Fig. 7 is a side schematic cross-sectional view of an exemplary transfer article including an exemplary retroreflective article, wherein the transfer article is shown coupled to a substrate.

Fig. 8a is a photograph of a scanning electron microscope secondary electron 200 × of an exemplary reference example article including a carrier layer carrying transparent microspheres with a primary reflective layer disposed thereon.

Fig. 8b is a scanning electron microscope backscattered electron 200x photograph of a portion of the same reference example article as fig. 8 a.

Fig. 9a is a scanning electron microscope secondary electron 500 × photograph of a portion of an exemplary reference example article including a carrier layer carrying transparent microspheres with a primary reflective layer disposed thereon.

Fig. 9b is a scanning electron microscope backscattered electron 500 × photograph of a portion of the same reference example article as fig. 9 a.

Fig. 10a is a scanning electron microscope secondary electron 1000 × photograph of a portion of an exemplary reference example article including a carrier layer carrying transparent microspheres with a primary reflective layer disposed thereon.

Fig. 10b is a scanning electron microscope backscattered electron 1000 × photograph of a portion of the same working example article as fig. 10 a.

Fig. 11 is an optical microscope photograph of a portion of an exemplary reference example article including a carrier layer carrying transparent microspheres with a primary reflective layer disposed thereon.

Like reference symbols in the various drawings indicate like elements. Some elements may be present in the same or equal multiples; in this case, one or more representative elements may be designated by reference numerals only, but it should be understood that such reference numerals apply to all such identical elements. Unless otherwise indicated, all non-photographic and drawing figures in this document are not drawn to scale and are chosen for the purpose of illustrating different embodiments of the invention. In particular, unless otherwise specified, dimensions of various components are described in terms of illustrative terms only, and relationships between dimensions, relative curvatures, and the like of the various components should not be inferred from the drawings.

As used herein, terms such as "front", "forward", and the like refer to the side of the retroreflective article from which it is viewed. Terms such as "rear", "rearward", and the like refer to opposite sides, e.g., to be attached to one side of a garment. The term "lateral" refers to any direction perpendicular to the front-to-back direction of the article and includes directions along both the length and width of the article. The front-to-back direction (f-r) and exemplary lateral direction (1) of the exemplary article are shown in fig. 1.

Terms such as disposed above (on), above (upon), on top of (atop), between (between), behind (behind), adjacent to (adjacent), contacting (contact), near (proximity), etc., do not require that a first entity (e.g., layer) must be in direct contact with a second entity (e.g., second layer) on which the first entity is disposed, behind, adjacent to, or in contact with. Rather, such terms are used for convenience of description and allow for the presence of additional entities (e.g., layers such as bonding layers) or entities therebetween, as will be apparent from the discussion herein.

As used herein, the term "substantially", as a modifier to an attribute or trait, unless specifically defined otherwise, means that the attribute or trait would be readily identifiable by a person of ordinary skill without requiring a high degree of approximation (e.g., within +/-20% for quantifiable attributes). For angular orientation, the term "substantially" means within 10 degrees of clockwise or counterclockwise. Unless specifically defined otherwise, the term "substantially" means highly approximate (e.g., within +/-10% for quantifiable attributes). With respect to angular orientation, the term "substantially" means within 5 degrees of clockwise or counterclockwise. The term "substantially" means highly approximated (e.g., within +/-2% for quantifiable properties; within +/-2 degrees for angular orientation); it should be understood that the phrase "at least substantially" includes the particular case of an "exact" match. However, even where "exact" matches, or where any other characterization is used in terms such as, for example, identical, equal, consistent, uniform, constant, etc., are to be understood as being within ordinary tolerances, or within measurement error applicable to the particular situation, rather than requiring an absolutely exact or perfect match. The term "configured to" and similar terms are at least as limiting as the term "adapted to" and require the actual design intent to perform the specified function, not just the physical ability to perform such function. All references herein to numerical parameters (dimensions, ratios, etc.) are understood to be able to be calculated (unless otherwise stated) by using the average of multiple measurements derived from the parameter. All averages referred to herein are number average unless otherwise indicated.

Detailed Description

Fig. 1 shows a retroreflective article 1 in an exemplary embodiment. As shown in fig. 1, the article 1 includes an adhesive layer 10, the adhesive layer 10 including a plurality of retroreflective elements 20 spaced apart in the length and width of the front side of the adhesive layer 10. Each retroreflective element includes transparent microspheres 21 partially embedded in the binder layer 10 such that the microspheres 21 are partially exposed and define the front (viewing) face 2 of the article. Thus, the transparent microspheres each have an embedded region 25 and an exposed region 24, the embedded region 25 being disposed in the receiving cavity 11 of the adhesive layer 10, the exposed region 24 being exposed (protruding) in front of the major front surface 14 of the adhesive layer 10. In some embodiments, the exposed areas 24 of the microspheres 21 of the article 1 are exposed to the ambient atmosphere (e.g., air) in the final article of use, rather than, for example, being covered with any kind of cover layer or the like. Such articles will be referred to as exposed lens retroreflective articles. In various embodiments, the microspheres may be partially embedded in the binder layer such that, on average, 15%, 20%, or 30% of the diameter of the microspheres are embedded within the binder layer 10 to about 80%, 70%, 60%, or 50% of the diameter of the microspheres. In many embodiments, the microspheres may be partially embedded in the binder layer such that, on average, 50% to 80% of the microsphere diameter is embedded within the binder layer 10.

Primary and secondary reflective layers

The retroreflective element 20 will include a primary reflective layer 30, the primary reflective layer 30 being disposed between the transparent microspheres 21 and the binder layer 10 of the retroreflective element and the primary reflective layer covering (e.g., disposed on) the portions 28 of the embedded regions 25 of the transparent microspheres. The retroreflective element 20 will also include a secondary reflective layer 180. The secondary reflective layer 180 is provided by a layer of adhesive layer 10, the adhesive layer 10 being adjacent to the portion 27 of the embedded region 25 not covered by the primary reflective layer 30, as shown in fig. 1 and 3. Secondary reflective layer 180 includes reflective particles 179, as shown in fig. 3 and discussed in detail later herein. It is to be understood that the primary reflective layer 30 is a separate component from the adhesive layer 10, and thus is distinguished from the secondary reflective layer 180 obtained by including the reflective particles 179 in the adhesive layer 10.

The transparent microspheres 21 and the primary reflective layer 30 (and in some cases, the secondary reflective layer 180) collectively return a significant amount of incident light to a light source that impinges on the front side 2 of the article 1. That is, light that strikes the front side 2 of the retroreflective article enters and passes through the microspheres 21 and is reflected by the reflective layer to re-enter the microspheres 21 again such that the light is directed back toward the light source.

Embedded primary reflective layer

As shown in the exemplary embodiment of fig. 1, at least some of the primary reflective layer 30 in the retroreflective elements 20 of the retroreflective article 1 will be embedded reflective layers. In various embodiments, at least substantially, or substantially all of the primary reflective layer 30 of the retroreflective element 20 can be an embedded reflective layer.

The embedded reflective layer 30 is a reflective layer disposed adjacent to portions of the embedded regions 25 of the transparent microspheres 21, as shown in the exemplary embodiment of fig. 1. The embedded reflective layer will at least substantially conform to the portion (often including the last portion) of the embedded region 25 of the transparent microspheres 21. By definition, the embedded reflective layer will be completely surrounded (e.g., sandwiched) by at least the combination of the binder layer 10 and the transparent microspheres 21 (note that in some embodiments, some other layer(s), e.g., intervening layers, such as adhesive layers and/or color layers, may also be present in the article 1, as discussed later herein, and may facilitate the surrounding of the reflective layer). In other words, the tiny edges 31 of the reflective layer (as shown in the exemplary embodiment of FIG. 1) will be "buried" between the transparent microspheres 21 and the binder layer 10 (and possibly other layers) rather than being exposed. That is, locations 26 that mark the boundary between exposed regions 24 of microspheres and embedded regions 25 of microspheres will be bordered by edges 16 of adhesive layer 10 (or the edges of the layers disposed thereon), rather than by tiny edges 31 of reflective layer 30.

For transparent microspheres 21 that include an embedded reflective layer 30, no portion of the embedded reflective layer 30 is exposed so as to extend onto (i.e., cover) any portion of the exposed area 24 of the microspheres 21. Thus, microspheres with embedded reflective layer 30 are distinguished from arrangements made by a "randomized bead" process, wherein the microspheres are hemispherically coated with a reflective layer and then randomly disposed on a substrate such that many microspheres exhibit an at least partially exposed reflective layer. Further, retroreflective elements that include an embedded reflective layer 30 as disclosed herein will be distinguished from arrangements in which microspheres that have been coated with a reflective layer over the entire surface of the microspheres are disposed on a substrate, after which the reflective layer is removed from the exposed areas of the microspheres, for example, by etching. Such an arrangement does not cause the reflective region to exhibit a "buried" edge and therefore does not result in an embedded reflective layer as defined herein.

It should be understood that in actual commercial production of retroreflective articles of the general type disclosed herein, small-scale statistical fluctuations may inevitably exist, which may result in the formation of a very small amount of reflective layer, e.g., micro-segments, that exhibit micro-edges or areas that are exposed rather than buried. Such occasional occurrences would be expected in any realistic production process; however, an embedded reflective layer as disclosed herein is distinguished from a situation in which the reflective layer is purposefully arranged in such a way that it will exhibit a large number of exposed tiny edges or regions.

Partial/bridging main reflective layer

In some embodiments, the primary reflective layer 30 will be a partially reflective layer. By definition, the partially reflective layer is a primarily reflective layer that does not include any portion that extends to any significant degree from the embedded region 25 of the microspheres 21 along any lateral dimension of the article 1. In particular, the partially reflective layer will not extend laterally to bridge the lateral gap between adjacent transparent microspheres 21. In some embodiments, at least substantially, or substantially all (according to the definition provided previously) of the primary reflective layer 30 will be a partially reflective layer. However, in some particular embodiments (e.g., involving a laminated reflective layer as discussed later herein), the primary reflective layer may bridge the lateral gap between adjacent transparent microspheres. In such cases, the reflective layer may be sized and positioned such that a portion of the reflective layer is positioned at least substantially behind a transparent microsphere and another portion of the same reflective layer is positioned at least substantially behind another adjacent microsphere. Thus, a single reflective layer may operate in conjunction with two (or more) transparent microspheres, and will be referred to as a "bridging" reflective layer. The bridging reflective layer is not a partially reflective layer as defined herein, however, the peripheral edge of the bridging reflective layer is buried between the transparent microspheres and the binder material; thus, the bridging reflective layer is an "embedded" reflective layer. An exemplary primary reflective layer that is a bridging reflective layer (which appears dark in the optical photograph) is identified by reference numeral 36 in the photograph of the working example sample presented in fig. 11; the bridging reflective layer appears to bridge three transparent microspheres.

The presence of a bridging reflective layer appears to be statistically driven and influenced by, for example, lamination conditions (as discussed in U.S. provisional patent application 62/739,506; attorney docket No. 81159US002, entitled "retroreflective article comprising a partially laminated reflective layer," and incorporated by reference herein in its entirety). In some implementations, any such bridging reflective layer (if present) can represent a relatively small fraction of the total number of primary reflective layers. Thus, in some embodiments, the bridging reflective layer may be present at a level of less than 20%, 10%, 5%, 2%, or 1% of the total amount of the primary reflective layer. However, in some particular embodiments, the bridging reflective layer may represent up to 20%, 30%, 40%, or even 50% or more of the total amount of the primary reflective layer.

FIG. 2 is an enlarged isolated perspective view of transparent microspheres 21 and an exemplary embedded primary reflective layer 30, wherein the adhesive layer 10 is omitted for ease of visualizing the reflective layer 30. FIG. 3 is an enlarged isolated side schematic cross-sectional view of transparent microspheres and partially embedded primary and secondary

reflective layers

30 and 180 achieved by including reflective particles 179 in binder layer 10. As shown in these figures, the embedded primary reflective layer 30 will include a major forward surface 32 that often exhibits a generally arcuate shape, such as portions where at least a portion of the forward surface 32 at least generally conforms to the major rearward surface 23 of the microspheres 21. In some embodiments, the major forward surface 32 of the reflective layer 30 may be in direct contact with the major rearward surface 23 of the microspheres 21; however, in some embodiments, the major forward surface 32 of the reflective layer 30 may contact a layer that is itself disposed on the major rearward surface 23 of the microspheres 21, as discussed in further detail later herein. The layer provided in this way may be, for example, a transparent layer, which serves, for example, as a protective layer, bonding layer or adhesion-promoting layer; alternatively, such layers may be color layers as discussed in detail later herein. The major rearward surface 33 of the primary reflective layer 30 (e.g., the surface in contact with the forward surface 12 of the adhesive layer 10 as shown in fig. 1, or the surface of the layer present thereon) can, but need not, at least generally coincide with (e.g., be partially parallel to) the major forward surface 32 of the reflective layer 30. This may depend, for example, on the particular manner in which the reflective layer is disposed on the transparent microspheres, as discussed later herein.

Percent area coverage of the primary reflective layer

As is evident from fig. 2 and 3, the primary reflective layer 30, which is an embedded reflective layer, will be positioned such that it occupies (covers) a portion 28, but not all, of the embedded region 25 of microsphere 21. The remainder of the embedded region 25 will be the region 27 not occupied by the reflective layer 30. Such an arrangement may be characterized in terms of the percentage of embedded region 25 covered by primary reflective layer 30 (whether layer 30 is in direct contact with region 25 or separated therefrom by, for example, a bonding layer or the like). In various embodiments, the primary reflective layer, if present on the microspheres, may occupy a cover portion 28, the cover portion 28 being at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70% of the embedded region 25 of the microspheres. In further embodiments, the primary reflective layer (if present) may occupy the cover portion 28, the cover portion 28 being at most 95%, 85%, 75%, 60%, 55%, 45%, 35%, 25%, or 15% of the embedded region 25. Such calculations would be based on the actual percentage of multi-dimensional curved embedded region 25 covered by reflective layer 30, rather than using, for example, a planar projection area. By way of specific example, the exemplary reflective layer 30 of fig. 3 occupies a portion 28, which portion 28 is estimated to be approximately 20% to 25% of the embedded region 25 of the microsphere 21.

In some embodiments, the embedded primary reflective layer 30 can be characterized in terms of the percentage of the total surface area of the microsphere that is occupied (covered) by the reflective layer (i.e., embedded regions 25 plus exposed regions 24). In various embodiments, the primary reflective layer, if present on the microspheres, may occupy a coverage area that is at least 5%, 10%, 15%, 20%, 25%, 30%, or 35% of the total surface area of the microspheres. In further embodiments, the primary reflective layer (if present) can occupy a coverage area that is less than 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, or 10% of the total surface area of the microspheres. By way of specific example, the exemplary reflective layer 30 of FIG. 3 is estimated to occupy an area 28, which area 28 is approximately 10% to 12% of the total surface area of the microsphere 21.

Such angular arcs α may be taken along a cross-sectional slice of the transparent microspheres (e.g., resulting in a cross-sectional view such as that shown in fig. 3) and may be measured from an apex (v) at the geometric center of the transparent microspheres 21, as shown in fig. 3. in various embodiments, the embedded primary reflective layer 30 may be disposed such that it occupies an angular arc α that includes less than 180, 140, 100, 80, 60, 40, or 30 degrees.

As will be apparent from the detailed discussion later herein regarding the method of making the primary reflective layer, in many embodiments, the primary reflective layer 30 is not necessarily symmetrical (e.g., circular and/or centered on the front-to-back centerline of the transparent microsphere) when viewed along the front-to-back axis of the transparent microsphere. Rather, in some cases, the primary reflective layer 30 may be non-circular, e.g., oval, irregular, offset, stippled, etc., in the general manner shown in the general representation of fig. 4. Thus, if such a reflective layer is characterized by angular arcs in the manner described above, the average of the angular arcs will be reported. Such an average may be obtained, for example, by measuring the angular arc at several (e.g., four) locations around the microsphere (with the microsphere viewed along its anteroposterior axis) as shown in fig. 4 and averaging these measurements. (such methods may also be used to obtain the area percentages noted above).

For a primary reflective layer positioned symmetrically on the microsphere, for example as shown in fig. 1-3, the midpoints of any or all such angular arcs may at least substantially coincide with the front-to-back axis (centerline) of the microsphere. That is, for a primary reflective layer that is both symmetrically positioned and symmetrically shaped, the geometric center of the reflective layer may coincide with the front-to-back centerline of the microsphere. However, in some embodiments, the reflective layer may be at least slightly offset relative to the front-to-back centerline of the microsphere such that at least some of such midpoints may be located, for example, 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, or 85 degrees away from the front-to-back centerline of the microsphere.

The primary reflective layers of different microspheres may differ from each other in shape and/or size, except for any single primary reflective layer that may exhibit an irregular shape in fig. 4. For example, in some embodiments, the primary reflective layer may be conveniently disposed on the microspheres by transfer to protruding portions of the microspheres while the microspheres are partially (and temporarily) embedded in the carrier. Since different microspheres may vary slightly in diameter and/or may vary in depth of embedding within the carrier, different microspheres may protrude outward from the carrier by different distances. In some cases, microspheres that protrude further outward from the carrier may receive a greater amount of the reflective layer transferred thereto than microspheres that are embedded deeper into the carrier. In this case, it should be understood that the primary reflective layers of the various microspheres may differ from one another in the angular arc occupied by the reflective layer and/or in the percentage of the embedded region of the microspheres (or the percentage of the total area of the microspheres) occupied by the reflective layer.

Despite such variations, it should be understood that retroreflective elements including an embedded primary reflective layer as disclosed herein are distinguished from arrangements in which transparent microspheres hemispherically covered with a reflective layer are randomly (e.g., by a so-called "randomized bead" process) disposed onto a binder layer. That is, an embedded reflective layer as disclosed herein will tend to collect on or near the rearmost portion of the microsphere; alternatively, if the reflective layers are offset from this last portion, they will tend to be offset in the same direction. In contrast, the randomized bead approach will produce a reflective layer that is widely distributed over all possible angular orientations on the microsphere surface.

The primary reflective layer can exhibit any suitable thickness (e.g., an average thickness measured at several locations within the reflective layer). It should be understood that different methods of making the reflective layer may produce reflective layers of different thicknesses. In various embodiments, the primary reflective layer can exhibit an average thickness (e.g., measured at several locations within the reflective layer range) of at least 0.01, 0.05, 0.1, 0.2, 0.5, 1, 2, 4, or 8 microns up to 40, 20, 10, 7, 5, 4, 3, 2, or 1 microns. In various embodiments, the primary reflective layer can include an average thickness of at least 10 nanometers, 20 nanometers, 40 nanometers, or 80 nanometers; in further embodiments, such reflective layers may comprise an average thickness of up to 10 microns, 5 microns, 2 microns, or 1 micron, or an average thickness of up to 400 nanometers, 200 nanometers, or 100 nanometers. These thicknesses only apply to the reflective layer itself if the reflective layer (or, for example, a set of sub-layers of a dielectric stack that together provide the reflective layer) is a layer of a multi-layer stack (a transfer stack as described later herein).

Sub-reflecting layer

Retroreflective element 20 that includes the primary reflective layer 30 described above will also include a secondary reflective layer 180. This is achieved by loading the binder layer 10 with reflective particles 179 (e.g., flakes) of a reflective material (e.g., pearlescent or beaded material). This may provide that at least a portion of the binder layer 10 adjacent to the transparent microspheres 21 may serve as a secondary reflective layer 180, as shown in fig. 1, and in further detail in fig. 3. By secondary reflective layer is meant the portion of the binder layer 10 that is used to enhance the performance of the retroreflective elements 20 above that provided by the primary reflective layer 30 covering the regions 28 of the transparent microspheres 21 of the retroreflective elements. By definition, secondary reflective layer 180 is adjacent to and cooperates with portions 27 of embedded region 25 of transparent microspheres 21 not covered by primary reflective layer 30. Such a secondary reflective layer 180 (which does not necessarily have a well-defined rearward boundary) may provide at least some retroreflection due to the focusing effect of the reflective particles 179 present in that layer. The secondary reflective layer may not necessarily provide the same amount and/or quality of retroreflection as provided by the primary reflective layer 30. However, the secondary reflective layer may provide, for example, that areas 27 of the transparent microspheres not covered by the primary reflective layer 30 may still exhibit enhanced retroreflectivity. Thus, in some embodiments, primary reflective layer 30 may provide excellent retroreflectivity, for example, at general "face" angles, while secondary reflective layer 180 may enhance retroreflectivity at high or glancing angles ("declination") of incident light. Further, where the binder layer of the article includes a colorant, such retroreflective performance can be achieved while maintaining excellent color fidelity, as discussed in detail later herein.

To achieve such an effect, the adhesive layer 10 may be loaded with an appropriate amount of reflective particles 179. In various embodiments, the reflective particles may be present in the binder at a loading of at least 0.05 wt%, 0.10 wt%, 0.20 wt%, 0.50 wt%, 1.0 wt%, 2.0 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, or 7.0 wt%. In further embodiments, the reflective particles may be present in the binder at a loading of less than 30 wt.%, 20 wt.%, or 10 wt.%. In some embodiments, the reflective particles will be present in the binder at a loading of less than 8.0 wt.%, 7.5 wt.%, 7.0 wt.%, 6.5 wt.%, 5.5 wt.%, or 4.5 wt.%. (all such loadings are on a dry solids basis and do not contain any liquid or volatile material that does not remain in the binder layer). In various embodiments, the reflective particles can include an average particle size (diameter or effective diameter) of at least 5 microns, 10 microns, 20 microns, or 30 microns; in further embodiments, the reflective particles may comprise an average particle size of up to about 200 microns, 150 microns, 100 microns, or 50 microns. It is noted that in many embodiments, the reflective particles may be, for example, flake-like, having a high aspect ratio, for example, greater than 2.0, 4.0, or 8.0. In such cases, the reflective particles may comprise, on average, a longest dimension of at least 5 microns up to 200 microns.

In some embodiments, it may be particularly advantageous to select the average particle size of the reflective particles (or average longest dimension in the case of high aspect ratio particles) in the binder to be less than the average particle size (diameter) of the transparent microspheres. Thus, in various embodiments, the average particle size of the reflective particles in the binder may be no more than 40%, 20%, 10%, or 5% of the average particle size of the transparent microspheres.

In various particular embodiments, the secondary reflective layer 180 resulting from the presence of the reflective particles 179 in the binder layer 10 may be used in combination with the primary reflective layer 30, the primary reflective layer 30 exhibiting a percent area coverage (i.e., including the covered portions 28 of the embedded regions 25) of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, or even 10% of the embedded regions of the microspheres. In various embodiments, such secondary reflective layers can be used in combination with primary reflective layers exhibiting an angular arc of less than 80 degrees, 60 degrees, 50 degrees, 40 degrees, 30 degrees, 20 degrees, or 10 degrees.

Suitable reflective particles may be selected from, for example, metal flakes (such as aluminum or silver flakes), pearlescent pigment flakes (such as BiOCl), TiO₂Coated mica, oxide coated glass flake, hexagonal PbCO₃Particles, oxide coated fluorophlogopite platelets, and crystalline guanine platelets (e.g., obtained from fish scales). Products which may be particularly suitable include, for example, those available under the trade names MEARELITE (e.g. MEARELITE ULTRA BRIGHT UTL) from BASF SE (Ludwigshafen am Rhein, Germany) of Lodvieh, Ridgel, Germany, and those available under the trade names LUXAN B001 and SYMIC C001 from Wessel Ekhart, Germany (Ekhart (Altana AG), Wesel, Germany). In some embodiments, the binder layer 10 will include less than 8.0 wt%, 7.5 wt%, 7.0 wt%, 6.0 wt%, 5.0 wt%, 4.0 wt%, 2.0 wt%, 1.5 wt%, 0.8 wt%, 0.4 wt%, 0.3 wt%, or 0.15 wt% (on a total dry solids basis) of any type of pearlescent reflective particles (e.g., BiOCl, PbCO)₃Guanine, etc.).

The arrangement disclosed herein provides transparent microspheres with a primary reflective layer 30, which primary reflective layer 30 occupies a smaller, sometimes much smaller, portion 28 of embedded region 25 than the total embedded region 25 of transparent microspheres 21. The secondary reflective layer 180 will be present adjacent to the portion 27 of the embedded region that is not covered by the primary reflective layer. This can provide significant advantages in at least some embodiments. For example, the primary reflective layer can provide excellent retroreflective performance under typical head-on conditions (e.g., light impinging on the microspheres generally along the front-to-back axis of the article). The secondary reflective layer may provide enhanced retroreflectivity at off angles. Also, the fact that the primary reflective layer does not cover the entire embedded region of the microspheres, and the fact that the secondary reflective layer is provided by discrete particles rather than by a continuous reflective entity, may provide that the presence of the reflective layer does not significantly detract from the appearance of the article in ambient light. That is, in ambient light, the article may exhibit an appearance that is imparted to a large extent by the composition of the binder, and in particular by any colorants or patterns that may be present in the binder, rather than an appearance that is dominated by the presence of the reflective layer.

In more detail, for retroreflective articles in which the entire embedded area of all of the microspheres of the article are covered by a continuous (e.g., primary) reflective layer, the reflective layer can dominate the appearance of the article in ambient light (e.g., such that the article exhibits a gray or washed-out appearance). In contrast, the arrangement of the present invention may provide a "natural" color of the article, e.g., the color as imparted by one or more colorants disposed in the binder layer, may be perceived in ambient light. In other words, enhanced color fidelity or freshness may be provided in ambient light.

It should therefore be appreciated that the arrangements disclosed herein allow a designer of retroreflective articles to operate in a design space where the retroreflective performance of the article over a variety of angles and the color/appearance in ambient light can be manipulated. While there may be some trade-offs (e.g., retroreflectivity may increase as color fidelity decreases, and vice versa), the design space is such that acceptable values for both parameters may be obtained and may be tailored to the particular application.

"non-uniform" primary reflective layer

The arrangement of the present invention allows for and even exploits significant variability in the primary reflective layer. That is, as is apparent from the discussion herein, at least some methods of forming the primary reflective layer can result in significant variability in the percent area coverage (i.e., in the size of the primary reflective layer coverage area 28 relative to the embedded region 25) that the primary reflective layer exhibits on the microsphere population. This is evidenced by the variability in the size of the area 28 covered by the reflective layer 30 in the scanning electron micrographs (at various magnifications) of the various reference example samples presented in fig. 8 a/8 b, 9 a/9 b and 10 a/10 b. The "a" map is obtained via secondary electron imaging, which provides more visual detail. The "b" plot is the same image, but obtained via electron backscattering, where high atomic number elements appear as very bright (white) colors. (in the sample of the specific reference examples presented in these figures, the reflective layer is metallic silver, which appears very white compared to the darker color of the glass microspheres and various organic polymer layers in the "b" figure).

All of these figures (as well as fig. 11) consist of a carrier-loaded microsphere 21, the microsphere 21 having an intervening layer 50 (described later herein) and a primary reflective layer 30 disposed thereon but not yet formed with a binder layer 10. Therefore, these samples also have no sub-reflective layer formed therein, and are therefore referred to as reference examples. However, these figures are considered to be representative of how the microspheres and the primary reflective layer are arranged after the binder layer is formed thereon. The occasional dark cavities visible in these figures are formed by through holes in the intervening layer 50, where the layer precursor does not wet completely into the interstices between the microspheres 21, so the surface of the carrier layer 110 is visible (and dark) through the resulting pores in the intervening layer.

As described above, fig. 8 a/8 b, 9 a/9 b and 10 a/10 b (and fig. 11) reveal considerable variations in the area coverage exhibited by the different reflective layers. The specific samples shown in these figures were all obtained by a physical transfer (lamination) method; however, other methods (e.g., printing and deposition/etching) also impart considerable variation in the area coverage exhibited by the reflective layer. In addition, as is evident from the higher magnification micrographs of fig. 9 a/9 b and 10 a/10 b, the transfer reflective layer in many cases exhibits many discontinuities (e.g., cracks and gaps) in the nominal total area covered by the reflective layer. Such gaps may be ignored for calculating the percent area coverage previously discussed if they are relatively insignificant (e.g., if they do not change the calculated area coverage by more than 10%). However, if such gaps would greatly affect the calculated area coverage, they should be considered. However, the nominal outer perimeter of the reflective layer may be used to calculate the angular arc previously discussed without regard to any such gaps.

Thus, it should be understood that the percent area coverage (and resulting overall size) exhibited by different primary reflective layers, as well as the amount and/or size of gaps within different primary reflective layers, may vary considerably for a large number of retroreflective elements. (based on the foregoing discussion, it should be understood that the non-photographic figures of the present patent application are idealized representations in which the variations described above are not shown for ease of presentation). Surprisingly, despite such non-uniformity of the primary reflective layer, acceptable or even excellent retroreflective performance can be obtained. In various embodiments, the percent area coverage of the embedded region of transparent microspheres by the primary reflective layer may exhibit a coefficient of variation (obtained by standard statistical techniques and expressed in decimal scale) greater than zero when evaluated on a statistically suitable sample of microspheres from the total microsphere population. By way of specific example, a group of microspheres whose reflective layer exhibits an average percent area coverage of 44% and a standard deviation of 26% (in the same units as the average) would exhibit a coefficient of variation of 0.59. A primary reflective layer having a percent area coverage (embedded regions of microspheres) that exhibits a coefficient of variation greater than 0.05 will be referred to herein as a "non-uniform" primary reflective layer. In various embodiments, the non-uniform primary reflective layer can be configured such that the percent area coverage of the embedded regions of the transparent microspheres by the primary reflective layer exhibits a coefficient of variation greater than 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.80, 1.0, 1.2, 1.4, or 2.0. In a similar manner, the coefficient of variation of the percent area coverage of the total surface area of the transparent microspheres by the primary reflective layer can be calculated. In various embodiments, such coefficient of variation may be greater than 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.80, 1.0, 1.2, 1.4, or 2.0. In a similar manner, the coefficient of variation of the aforementioned angular arc occupied by the primary reflective layer may be calculated. In various embodiments, such coefficient of variation may be greater than 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.80, 1.0, 1.2, 1.4, or 2.0.

It should be understood that the large number of non-uniform primary reflective layers as defined and described herein are significantly different from the conventional population of uniform reflective layers as often described in the art. Conventional approaches (whether using transparent microspheres, prismatic elements such as cube corners, etc.) typically attempt to achieve as much uniformity in geometric parameters as possible. The skilled person will appreciate that the conventional procedure wherein the transparent microspheres are partially embedded in a temporary carrier, the protruding portions of the microspheres are provided with a reflective layer by a deposition method that is at least substantially uniform over a large area, and then a binder layer is formed thereon, does not result in a non-uniform reflective layer as defined and described herein. Examples of at least substantially uniform deposition methods (i.e., methods that "mask" a substantial number of protruding portions of the microspheres with a reflective coating in a substantially uniform manner) that one of ordinary skill would not desire to provide a non-uniform reflective coating include, for example, vacuum deposition, vapor coating, sputter coating, electroless plating, and the like (when performed without any masking, subsequent etching, or any such action that might impose variations). Specific examples of reflective layers that exhibit such high uniformity as to appear to exhibit a zero coefficient of variation and thus are not compatible with a non-uniform reflective layer as defined herein include, for example, the reflective layers depicted in U.S. patents 3700305, 4763985, and 5344705.

Thus, it is apparent that the methods disclosed herein are distinct from conventional methods of producing retroreflective articles. The inventive arrangement allows and even welcomes significant variations in shape, size, etc. of the various primary reflective layers, as long as acceptable overall performance (in particular, a balance between retroreflectivity in retroreflected light and color fidelity/freshness in ambient light) is achieved. Further, in at least some embodiments, it is not required that the reflective layers be continuous and defect-free (i.e., no through-holes), but at least some of the primary reflective layers may include discontinuities (e.g., holes, cracks, or gaps) such that they optically "leak".

Lack of main reflecting layer

Additionally, in some embodiments, the plurality of transparent microspheres may be completely free of the primary reflective layer. (microspheres without a primary reflective layer would not be included in the statistical analysis described above to obtain a coefficient of variation in percent area coverage for the reflective layer population). That is, some methods of reflective layer formation may leave a large number of microspheres without a primary reflective layer disposed thereon. Many of the transparent microspheres lacking the primary reflective layer were visible in the photograph of the working example sample shown in fig. 11; one such microsphere is identified by reference numeral 37 (the small white dots visible in the center of many such microspheres are optical artifacts of the microspheres themselves). For comparison purposes, randomly selected microspheres bearing a reflective layer are identified by reference numeral 20. It has been found that in many cases, the presence of transparent microspheres lacking a primary reflective layer is acceptable (e.g., a sufficiently high overall coefficient of retroreflectivity for the retroreflective article can still be obtained). In fact, such an arrangement may actually allow for the preservation of more of the "natural" color of a retroreflective article that includes a colorant-loaded binder. It should be understood that in the arrangements disclosed herein, a significant number of microspheres are intentionally deprived of the primary reflective layer, unlike, for example, the lack of an occasional, statistically driven reflective layer that may be present in any type of article described in the art.

In various embodiments, the retroreflective article can be configured such that the transparent microspheres comprising the primary reflective layer are less than 95%, 90%, 80%, 60%, 40%, 20%, or even 15% (by number) of the total transparent microspheres present in the retroreflective article. In other embodiments, the transparent microspheres comprising the primary reflective layer will be greater than 5%, 10%, 20%, 30%, 50%, 70%, or 80% of the total transparent microspheres present in the retroreflective article.

In some embodiments, the primary reflective layer 30 (e.g., an embedded and/or partially reflective layer) can include a metal layer, such as a single layer or multiple layers of vapor deposited metal (e.g., aluminum or silver). In some embodiments, such one or more layers (or precursors forming such layers) may be deposited directly onto regions 25 of transparent microspheres 21 (or onto rearward surface 53 of intermediate layer 50, or onto rearward surface 43 of color layer 40, as discussed later herein). In some implementations, portions of a previously deposited (e.g., continuous vapor deposited) reflective layer can be removed (e.g., by etching) to convert the reflective layer into a partially embedded primary reflective layer, as discussed in further detail later herein.

In some embodiments, the primary reflective layer (e.g., embedded and/or partially primary reflective layer) may comprise a dielectric reflective layer composed of an optical stack of high and low index layers that combine to provide reflective properties. The dielectric reflective layer is described in more detail in U.S. patent application publication 2017/0131444, which is incorporated by reference herein in its entirety for this purpose. In particular embodiments, the dielectric reflective layer may be a so-called layer-by-layer (LBL) structure, wherein each layer of the optical stack (i.e., each high refractive index layer and each low refractive index layer) is itself composed of a plurality of bi-layer sub-stacks. Each bilayer is in turn composed of a first sublayer (e.g., a positively charged sublayer) and a second sublayer (e.g., a negatively charged sublayer). At least one sub-layer of a bilayer of the high index sub-stack will include a component that imparts a high index of refraction, while at least one sub-layer of a bilayer of the low index sub-stack will include a component that imparts a low index of refraction. LBL structures, methods of making such structures, and retroreflective articles including dielectric reflective layers containing such structures are described in detail in U.S. patent application publication 2017/0276844, which is incorporated by reference herein in its entirety. In some embodiments, the primary reflective layer may thus comprise a plurality of sub-layers. In some implementations, a hybrid configuration may be used in which a metallic reflective layer and a dielectric reflective layer may be present, for example, as discussed in U.S. patent application publication 2017/0192142. In some embodiments, a layer of the transfer stack (e.g., a selective bonding layer or an embrittlement layer) may be used as a layer of the dielectric stack. Such an arrangement is described in U.S. provisional patent application 62/739,506, entitled "retroreflective article comprising a partially laminated reflective layer," attorney docket No. 81159US002, which will be mentioned in more detail later herein.

In some embodiments, the primary reflective layer (e.g., the embedded and/or partially reflective layer) can include a printed layer (e.g., including a reflective material such as metallic aluminum or silver). For example, a flowable precursor comprising one or more reflectivity-imparting materials (e.g., silver inks) can be disposed (e.g., printed) on portions 28 of regions 25 of microspheres 21 (or on a layer thereon), and then cured into a reflective layer. If desired, the printed (or otherwise provided) reflective layer can be heat treated (e.g., sintered) to enhance the optical properties of the reflective layer. In particular embodiments, the printed or coated reflective layer may also include particles, such as flakes, of reflective material (e.g., aluminum flake powder, pearlescent pigment, etc.). Various reflective materials that may be suitable for use are described in U.S. patent nos. 5344705 and 9671533, which are incorporated herein by reference in their entirety.

In some embodiments, the primary reflective layer (e.g., an embedded and/or partially reflective layer) can be a "partially laminated" reflective layer. Partially laminating a reflective layer refers to pre-forming the reflective layer into an article (e.g., as part of a film or sheet-like structure) and then physically transferring (i.e., laminating) localized areas of the pre-formed reflective layer to the portions of the transparent microspheres bearing the carrier. In some embodiments, the partially laminated reflective layer will be derived from a multilayer "transfer stack" comprising one or more additional layers in addition to the reflective layer. Additional layers may facilitate the transfer of the reflective layer to the transparent microspheres, as discussed in detail later herein. In various embodiments, some such additional layers may remain part of the resulting retroreflective article, and some may be sacrificial layers that do not remain part of the resulting retroreflective article.

Transfer laminates (referred to as transfer articles) are generally described in U.S. provisional patent application 62/478,992, which is incorporated herein by reference in its entirety. Partially laminated reflective layers of various constructions and configurations are described in detail in U.S. provisional patent application 62/578343 (for example, in example 2.3 (including examples 2.3.1 through 2.3.3) and example 2.4 (including examples 2.4.1 through 2.4.5), which is incorporated herein by reference in its entirety. Partially laminated reflective layers, methods of producing such layers, and methods in which such reflective layers can be identified and separated from other types of reflective layers are also described in detail in U.S. provisional patent application 62/739,506, entitled "retroreflective articles comprising partially laminated reflective layers," attorney docket No. 81159US 002; filed herewith and incorporated by reference herein in its entirety. In general, any reflective layer 30, such as any of the reflective layers of the types described above, may be disposed on the rearward surface of the portion 28 of the embedded region 25 of the transparent microspheres 21, or on the rearward surface of a layer present thereon (e.g., an intervening layer 50 or a colored layer 40 as described later herein).

As shown in the exemplary embodiment of fig. 5, in some embodiments, an intervening layer 50 (e.g., a transparent layer of organic polymeric material) may be provided such that part or all of the intervening layer is located rearward of the microspheres 21 and forward of at least a portion of the primary reflective layer 30. Thus, at least a portion of such an intervening layer 50 may be sandwiched between the microspheres 21 and the primary reflective layer 30, e.g., the forward surface 52 of the intervening layer 50 is in contact with the rearward surface of the embedded regions 25 of the microspheres 21, and the rearward surface 53 of the intervening layer 50 is in contact with the forward surface 32 of the primary reflective layer 30. In some embodiments, such a layer 50 may be continuous so as to have portions residing on the front surface 4 of the article 1 in addition to being present on the rearward face of the microspheres 21, as shown in the exemplary arrangement of fig. 5. In other implementations, such layers may be discontinuous (e.g., they may be partially embedded layers). Furthermore, even a "continuous" layer 50 may exhibit occasional through-holes or cavities at locations where the layer precursors do not fully wet into the interstices between the microspheres 21, as previously described.

Such an intervening layer may serve any desired function. In some embodiments, it may be used as a physical and/or chemical protective layer (e.g., to provide enhanced wear resistance, corrosion resistance, etc.). In some embodiments, such layers may function as a bonding layer (e.g., a tie layer or an adhesion promoting layer) that is capable of being bonded to by a reflective layer, as discussed later herein. It should be understood that some intervening layers may be used for more than one, such as all, of these purposes. In some embodiments, such an intervening layer may be transparent (in particular, it may be at least substantially free of any colorant, etc.). Organic polymer layers (e.g., protective layers) and potentially suitable compositions thereof are described in detail in U.S. patent application publication 2017/0276844, which is incorporated herein by reference in its entirety. In particular embodiments, such layers may be comprised of polyurethane materials. Various polyurethane materials that may be suitable for such purposes are described, for example, in U.S. patent application publication 2017/0131444, which is incorporated herein by reference.

As shown in the exemplary embodiment of fig. 6, in some embodiments, at least some of the retroreflective elements 20 can include at least one colored layer 40. The term "color layer" is used herein to denote a layer that preferentially allows electromagnetic radiation in at least one wavelength range to pass through, while preferentially minimizing the passage of electromagnetic radiation in at least one other wavelength range by absorbing at least some radiation in that wavelength range. In some implementations, the color layer will selectively allow visible light of one wavelength range to pass through while reducing or minimizing the passage of visible light of another wavelength range. In some implementations, the color layer will selectively allow visible light of at least one wavelength range to pass through while reducing or minimizing the passage of light in the near infrared (700nm to 1400nm) wavelength range. In some implementations, the color layer will selectively allow near infrared radiation to pass through while reducing or minimizing the passage of visible light of at least one wavelength range. A color layer as defined herein performs wavelength selective absorption of electromagnetic radiation by using a colorant (e.g., a dye or pigment) disposed in the color layer. Thus, the color layer is distinguished from the reflective layer (and from the clear layer) as one of ordinary skill would be familiar with the discussion herein.

Any such colored layer 40 can be arranged such that light retroreflected by the retroreflective elements 20 passes through the colored layer such that the retroreflected light exhibits the color imparted by the colored layer. Accordingly, the colored layer 40 can be disposed such that at least a portion of the layer 40 is located between the rearward surface 23 of the embedded region 25 of the transparent microspheres 21 and the forward surface 32 of the primary reflective layer 30 such that at least this portion of the colored layer 40 is located in the retroreflective light path. Thus, the forward surface 42 of color layer 40 may be in contact with the rearward surface of embedded region 25 of microspheres 21; also, the rear surface 43 of the color layer 40 may be in contact with the front surface of the main reflection layer 30. In some embodiments, in addition to color layer 40, the intervening layer (e.g., clear layer) 50 described above may also be present; such layers may be provided in any order (e.g., forward or rearward of the intervening layers) as desired. In some implementations, color layer 40 can serve some other function (e.g., as an adherable layer or tie layer) in addition to imparting color to retroreflected light.

In some embodiments, color layer 40 can be a discontinuous color layer, for example, a partial color layer as in the exemplary embodiment shown in fig. 6. In a particular implementation, the localized color layer 40 can be an embedded color layer (where the terms localized and embedded have the same meaning as described above). That is, embedded color layer 40 may include a tiny edge 41 that is "buried" rather than an exposed edge. In various implementations, the topical color layer can exhibit an average thickness (e.g., measured at several locations within the range of the color layer) of at least 0.1 micron, 0.2 micron, 0.5 micron, 1 micron, 2 microns, 4 microns, or 8 microns up to 40 microns, 20 microns, 10 microns, 7 microns, 5 microns, 4 microns, 3 microns, 2 microns, or 1 micron. In some embodiments, the intervening layer 50 may be provided with a colorant such that it functions as a color layer 40 (in addition to serving any or all of the functions described above).

The presence of a color layer (e.g., a partially embedded color layer) in at least some of the retroreflective light paths of the retroreflective article can allow article 1 to include at least some areas that exhibit colored retroreflected light regardless of the color exhibited by those areas (or any other areas of the article) in ambient (non-retroreflective) light. In some implementations, the reflective layer can be configured such that the entire reflective layer is positioned rearward of the color layer. This ensures that incident light does not reach (and reflect from) the reflective layer without passing through the color layer, regardless of the angle at which the light enters and exits the transparent microspheres. Such an arrangement can provide that the light retroreflected from the retroreflective element exhibits a desired color regardless of the angle of incidence/exit of the light. Such an arrangement can also have the color layer mask the reflective layer to advantageously enhance the color appearance in ambient (non-retroreflected) light. In other implementations, the reflective layer can be configured such that at least some portions of the reflective layer extend beyond the tiny edges of the color layer such that light can reflect from the reflective layer without passing through the color layer. Such an arrangement may provide that the retroreflected light may exhibit different colors depending on the incident/exit angle of the light.

The foregoing parameters (e.g., the angular arc occupied by the layer and the percentage of embedded area of the microspheres covered by the layer) can be used for characterization of the colored layer relative to the transparent microspheres and relative to the primary reflective layer with which the retroreflective optical path is shared. In various embodiments, at least some partially embedded color layers 40 can be disposed such that they each occupy an angular arc that includes less than about 190 degrees, 170 degrees, 150 degrees, 130 degrees, 115 degrees, or 95 degrees. In further implementations, at least some of the partially embedded color layers can each occupy an angular arc of at least about 5 degrees, 15 degrees, 40 degrees, 60 degrees, 80 degrees, 90 degrees, or 100 degrees. In various embodiments, at least some of the primary reflective layers can be disposed such that each primary reflective layer occupies an angular arc that is at least 5, 10, 15, 20, 25, or 30 degrees less than the angular arc of the partially embedded color layer with which it shares the retroreflecting light path. In other embodiments, at least some of the primary reflective layers can be disposed such that each primary reflective layer occupies an angular arc that is at least 5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees, or 30 degrees greater than the angular arc of the partially embedded color layer with which it shares the retroreflecting light path.

The article 1 may be arranged to provide for controlling the appearance of the article 1 in ambient (non-retroreflective) light as desired. For example, in the exemplary arrangement of fig. 1, the front surface 4 portion of the article 1 (e.g., in the area 25 of the front side 2 of the article 1 not occupied by the transparent microspheres 21) is provided by the visually exposed front surface 14 of the adhesive layer 10. In such embodiments, the appearance of the front side 2 of the article 1 in ambient light may thus be largely dominated by the color of the binder layer 10 (or lack thereof) in the regions 13 of the binder layer 10 lateral to between the microspheres 21. Thus, in some embodiments, the binder layer 10 may be a colorant-loaded (e.g., pigment-loaded) binder layer. The pigment may be selected to impart any suitable color in ambient light, such as fluorescent yellow, green, orange, white, black, and the like.

In some embodiments, the appearance of the retroreflective article 1 in ambient light can be manipulated, for example, by the presence and arrangement of one or more colored layers on the front side of the article 1. In some embodiments, any such colored layer, for example in combination with a binder loaded with a colorant, can be configured such that the front side of the article 1 exhibits a desired image when viewed in ambient light (this term broadly encompasses, for example, informational indicia, signage, aesthetic designs, etc.). In some embodiments, the article 1 can be configured (whether by manipulating the primary reflective layer and/or manipulating any colored layers in the retroreflected light path) to exhibit an image when viewed in retroreflected light. In other words, any arrangement that allows the appearance of the article 1 in ambient light to be manipulated (e.g., by using a colorant loaded binder, using a colorant loaded layer on the front side 4 of the article 1, etc.) is used in combination with any arrangement that can manipulate the appearance of the article 1 in retroreflected light (e.g., by using a colored layer, such as a partially embedded colored layer in the retroreflected light path).

Such arrangements are not limited to the specific exemplary combinations discussed herein and/or shown in the figures herein. Many such arrangements are discussed in detail in U.S. provisional patent application 62/675020, which is incorporated by reference in its entirety; it should be understood that any of the color arrangements discussed in the' 020 application can be used with the primary reflective layers disclosed herein.

Regardless of the particular color arrangement that may be used, it will be clear based on the discussion herein that the use of primary reflective layer 30, particularly those occupying a relatively small percentage (e.g., less than 60%) of the coverage area 28 of the embedded regions 25 of transparent microspheres 21, can significantly enhance the color fidelity of retroreflective article 1 (e.g., a reflective article that includes colorant-loaded binder layer 10) when viewed in ambient light. In other words, in ambient light, the article can exhibit a color that more closely matches the natural color of the binder loaded with the colorant (i.e., the article can exhibit a color that is similar to the color that the article would exhibit if it did not include any retroreflective elements).

Transfer article

In some embodiments, the retroreflective article 1 disclosed herein can be provided as part of a transfer article 100 that includes the retroreflective article 1 and a removable (disposable) carrier layer 110 that includes a front major surface 111 and a back major surface 112. In some convenient embodiments, the retroreflective article 1 can be constructed on such a carrier layer 110, as described later herein, the carrier layer 110 can be removed for the end use of the article 1. For example, the front side 2 of the article 1 may be in releasable contact with the back surface 112 of the carrier layer 110, as shown in the exemplary embodiment of fig. 7.

The retroreflective article 1 (e.g., still part of the transfer article 100) can be coupled to any desired substrate 130, as shown in fig. 7. This may be done in any suitable manner. In some embodiments, this may be accomplished by using a bonding layer 120 that couples the article 1 to a substrate 130, with the back side 3 of the article 1 facing the substrate 130. Such a bonding layer 120 may bond the adhesive layer 10 (or any layer disposed thereon rearwardly) of the article 1 to the substrate 130, for example, bonding one major surface 124 of the bonding layer 120 to the rear surface 15 of the adhesive layer 10 and bonding the other opposing major surface 125 of the bonding layer 120 to the substrate 130. Such bonding layer 120 may be, for example, a pressure sensitive adhesive (of any suitable type and composition) or a heat activated adhesive (e.g., an "on-iron" bonding layer). Various pressure sensitive adhesives are described in detail in U.S. patent application publication 2017/0276844, which is incorporated herein by reference in its entirety.

The term "substrate" is used broadly and encompasses any article, portion of an article, or collection of articles to which it is desirable to couple or mount the retroreflective article 1, for example. Further, the concept of a retroreflective article coupled to or mounted on a substrate is not limited to configurations in which the retroreflective article is attached to a major surface of the substrate, for example. Rather, in some embodiments, the retroreflective article can be, for example, a tape, a filament, or any suitable high aspect ratio article, such as threaded, woven, stitched, or otherwise inserted into and/or through the substrate such that at least some portion of the retroreflective article is visible. Indeed, such retroreflective articles (e.g., in the form of yarns) can be assembled (e.g., woven) with other, e.g., non-retroreflective articles (e.g., non-retroreflective yarns) to form a substrate in which at least some portions of the retroreflective article are visible. The concept of a retroreflective article coupled to a substrate thus encompasses situations in which the article effectively becomes part of the substrate.

In some embodiments, substrate 130 may be part of a garment. The term "garment" is used broadly and generally encompasses any item or portion thereof that is intended to be worn, carried, or otherwise present on or near the body of a user. In such embodiments, the article 1 may be directly coupled to the garment, for example, by the bonding layer 120 (or by stitching or any other suitable method). In other embodiments, the substrate 130 itself may be a support layer to which the article 1 is coupled, for example by bonding or stitching, and which adds mechanical integrity and stability to the article. The entire assembly including the support layer can then be attached to any suitable article (e.g., a garment) as desired. In general, it may be convenient for the carrier 110 to remain in place during the coupling of the article 1 to the desired entity, and then to be removed after the coupling is complete. Strictly speaking, when the carrier 110 is held in place on the front side of the article 1, the regions 24 of the transparent microspheres 21 will not have been exposed to air, and thus the retroreflective elements 20 may not have exhibited the desired level of retroreflectivity. However, an article 1 that is removably disposed on a carrier 110 for use in actually using the article 1 as a retroreflector would still be considered a retroreflective article as characterized herein.

Manufacturing method

In some convenient embodiments, retroreflective article 1 can be made by starting with a disposable carrier layer 110. The transparent microspheres 21 may be partially (and releasably) embedded in the carrier layer 110 to form a substantially single layer of microspheres. For such purposes, in some embodiments, carrier layer 110 may conveniently comprise a heat-softenable polymeric material, for example, which may be heated, and onto which the microspheres are deposited in such a way that they are partially embedded therein. The carrier layer may then be cooled so as to releasably maintain the microspheres in that condition for further processing.

Typically, the deposited microspheres are at least slightly laterally spaced from one another, although occasionally the microspheres may be in lateral contact with one another. The pattern of microspheres deposited on the support (i.e., the bulk density or proportional area coverage) will determine their pattern in the final article. In various embodiments, the microspheres may be present on the final article (whether throughout the article or in a macroscopic region of the article containing the microspheres) at a bulk density of at least 30%, 40%, 50%, 60%, or 70%. In further embodiments, the microspheres may exhibit a bulk density of up to 80%, 75%, 65%, 55%, or 45% (note that the theoretical maximum bulk density of monodisperse spheres on a flat surface is in the range of about 90%). In some embodiments, the microspheres may be provided in a predetermined pattern, for example, by using the methods described in U.S. patent application publication 2017/0293056, which is incorporated herein by reference in its entirety.

In various embodiments, the microspheres 21 may be partially embedded in the carrier 110, for example, to about 20% to 50% of the microsphere diameter. The regions 25 of the microspheres 21 that are not embedded in the carrier protrude outward from the carrier so that they can subsequently receive the reflective layer 30 and the binder layer 10 (and any other layers as desired). These regions 25 (which will form the embedded regions 25 of the microspheres in the final article) will be referred to herein as protruding regions of the microspheres during the time that the microspheres are disposed on the carrier layer in the absence of the binder layer. In conventional manufacturing processes, there may be some variation in the depth to which the different microspheres are embedded in the carrier 110, which may affect the size and/or shape of the reflective layer deposited onto portions of the protruding surfaces of the different microspheres.

An exemplary carrier layer comprising transparent microspheres is described in the working examples herein as a temporary bead carrier. Further details of suitable carrier layers, methods of temporarily embedding transparent microspheres in carrier layers, and methods of using such layers to produce retroreflective articles are disclosed in U.S. patent application publication 2017/0276844.

After the microspheres 21 are partially embedded in the carrier 110, a reflective layer (which will become the primary reflective layer after the binder layer 10 is formed, e.g., embedded in the primary reflective layer) may be formed on portions of the protruding regions 25 of at least some of the microspheres (again, the protruding regions 25 will become embedded regions after the binder layer 10 is formed). Embedding the reflective layer can be accomplished by any method that can form a reflective layer (or a reflective layer precursor that can be cured, e.g., by drying, curing, etc., to form the actual reflective layer), such that the reflective layer is embedded as defined and described herein.

In many convenient embodiments, the deposition process may be arranged to provide that the reflective layer is formed only on portions of the protruding regions 25 of the microspheres 21, rather than, for example, on the surface 112 of the carrier 110. For example, a contact transfer process (e.g., flexographic printing or lamination) may be used, wherein the reflective layer (or precursor) is contacted with the protruding regions of the microspheres such that the reflective layer is transferred to a portion of the protruding regions of the microspheres without transferring to the surface of the support to any significant extent. Any such process may be controlled such that the reflective layer (or precursor) is not disposed over the entire protruding regions 25 of the microspheres 21. That is, in some cases, the process may be carried out such that the reflective layer or precursor is transferred only to the outermost portions of the protruding regions 25 of the microspheres 21 (which will become the last portions of the embedded regions 25 of the microspheres 21 in the final article). In some cases, the reflective layer can be transferred to portions of the embedded regions that are larger than the portion that will be occupied by the reflective layer in the final article, after which portions of the reflective layer can be removed to leave only the desired region coverage.

By way of specific example with reference to fig. 3, microspheres 21 may be disposed on carrier 110 such that approximately 40% of the microsphere diameter is embedded in the carrier. Thus, the regions 25 of the microspheres 21 will protrude outwardly from the major surface of the carrier layer 110 to a maximum distance corresponding to about 60% of the diameter of the microspheres. A reflective layer forming (e.g., transferring) process may be performed such that the reflective layer covers only the outermost portions 28 of the protruding regions 25 of the microspheres (e.g., occupies an angular arc of about 80 degrees). After the reflective layer forming process is completed, the remaining portions 27 of the protruding regions 25 of the microspheres 21 will not include the reflective layer 30 thereon. In forming the binder layer 10, the retroreflective elements 20 will be formed that include microspheres 21 and a primary reflective layer 30, the primary reflective layer 30 being arranged in the general manner shown in fig. 3. That is, primary reflective layer 30 will cover only a generally rearward portion 28 of embedded region 25 of microspheres 21, and will not cover the remaining (e.g., forward) portion 27 of embedded region 25.

The primary reflective layer 30 may be disposed on portions of the protruding regions 25 of the (carrier) transparent microspheres 21 by any suitable method or combination of methods. This may be accomplished, for example, by vapor deposition of a metal layer (such as aluminum or silver), by depositing a number of high and low index layers to form a dielectric reflective layer, by printing (e.g., flexographic printing) or otherwise disposing a precursor including a reflective additive and then curing the precursor, by physically transferring (e.g., laminating) a pre-formed reflective layer, and the like. In particular embodiments, the printable ink may include precursor additives that can be converted into reflective materials. For example, the ink may include silver in a form (e.g., silver cations or as an organometallic silver compound) that, after being printed onto the desired areas, can undergo a chemical reaction (e.g., reduction) to form metallic silver that is reflective. Commercially available printable silver inks include, for example, PFI-722 conductive flexographic inks (Novacentrix, Austin, TX) and TEC-PR-010 inks (inctec, Gyeonggi-do, Korea), inc.

Thus, in some embodiments, the primary reflective layer 30 can be provided by printing a reflective ink or ink precursor on a portion of the protruding regions of the carrier-laden transparent microspheres. This general type of process in which the flowable precursor is deposited only on certain portions of the protruding regions of the microspheres will be characterized herein as a "printing" process. This is to be contrasted with a "coating" process, in which material is deposited not only on the protruding regions of the microspheres, but also on the support surface between the microspheres. In some convenient embodiments, such printing may comprise flexographic printing. Other printing methods may be used as an alternative to flexographic printing. Such methods may include, for example, pad printing, soft lithography, gravure printing, offset printing, and the like. In general, any deposition method (e.g., ink jet printing) can be used so long as the process conditions and flow properties of the reflective layer precursor are controlled such that the resulting reflective layer is an embedded (e.g., locally) reflective layer. It will be appreciated that whatever method is used, it may be advantageous to control the method so that the precursor is deposited in a very thin layer (e.g., a few microns or less) and at a suitable viscosity to provide that the precursor remains at least substantially in the region where it is deposited. Such an arrangement may ensure, for example, that the resulting primary reflective layer occupies the desired portion 28 of the embedded region 25 in the manner described above. It should also be understood that some deposition methods may provide a reflective layer in which the thickness may vary from place to place. In other words, the rearward major surface 33 of the primary reflective layer 30 may not necessarily be entirely coincident with the primary forward surface 32 of the reflective layer. However, it has been found that at least some amount of this type of variation (as may occur, for example, by flexographic printing) is acceptable in the working of the present invention.

In some embodiments, a primary reflective layer (e.g., a partially embedded primary reflective layer) 30 may be provided, for example, by forming a reflective layer on the support and microspheres thereon (e.g., by vapor coating of a metal, or by printing or coating a reflective ink), and then selectively removing (e.g., by etching) the reflective layer from the surface of the support and portions 27 of the protruding regions 25 of the microspheres (prior to forming any binder layer) to leave the partially reflective layer in place on the microspheres. In some particular embodiments of this type, an etch-resistant material (often referred to as a "resist") may be applied (e.g., by printing) on portions of the reflective layer that are located atop the protruding regions of the microspheres, but not on other portions of the reflective layer that reside on the microspheres, and not on the reflective layer that resides on the surface of the support. An etchant may then be applied that removes the reflective layer except for the portions protected by the resist. Such methods are described in more detail in U.S. provisional patent application 62/578343, which is incorporated herein by reference.

In some embodiments, the primary reflective layer (e.g., partially embedded primary reflective layer) 30 may be provided by a partial lamination process. The partial lamination process is a method in which a partial area of the pre-fabricated reflective layer is transferred to a portion of the protruding area of the transparent microspheres. In this process, local areas of the reflective layer are separated (interrupted) from areas of the reflective layer previously (in the pre-made reflective layer prior to lamination) laterally surrounding the transferred areas. The laterally surrounding areas of the reflective layer from which the localized areas are separated are not transferred to the microspheres (or any portion of the resulting article), but are removed from the vicinity of the microspheres (e.g., along with other sacrificial layers of a multilayer transfer stack of which the pre-formed reflective layer is a part). The partial lamination process is described in detail in the above-mentioned U.S. provisional patent application 62/739,529, entitled "retroreflective article comprising a partially laminated reflective layer," attorney docket No. 81159US 002; filed herewith and incorporated by reference herein in its entirety. Working examples of the present patent application also show the use of a partial lamination method.

After the formation of the reflective layer (and the deposition of any intervening layers 50 and/or color layers 40) that will ultimately become the primary reflective layer 30, a binder precursor (e.g., a mixture or solution of binder layer components) can be applied to the microsphere-bearing carrier layer 110. The binder precursor may be disposed onto the microsphere-loaded carrier layer, e.g., by coating, and then hardened to form a binder layer, e.g., a continuous binder layer. The binder can be any suitable composition, for example, it can be formed from a binder precursor that includes the elastomeric polyurethane composition, as well as any desired additives and the like. Binder compositions, methods of making binders from precursors, and the like are described in U.S. patent application publications 2017/0131444 and 2017/0276844, which are incorporated herein by reference in their entirety.

Generally, the binder layer 10 is configured to support the transparent microspheres 21 and is typically a continuous, fluid impermeable, sheet-like layer. In various embodiments, the adhesive layer 10 can exhibit an average thickness of 1 micron to 250 microns. In further embodiments, the adhesive layer 10 may exhibit an average thickness of 30 microns to 150 microns. The adhesive layer 10 may comprise a polymer containing units such as urethane, ester, ether, urea, epoxy, carbonate, acrylate, acrylic, olefin, vinyl chloride, amide, alkyd, or combinations thereof. A variety of organic polymer forming agents can be used to make the polymer. Polyols and isocyanates may react to form polyurethanes; the diamine compound and the isocyanate may react to form a polyurea; the epoxide may be reacted with a diamine or diol to form an epoxy resin, and the acrylate monomer or oligomer may be polymerized to form a polyacrylate; and the diacid can be reacted with a diol or diamine compound to form a polyester or polyamide. Examples of materials that may be used to form the adhesive layer 10 include, for example: vitel, available from Bostek Inc., Middleton, Mass. (Bostik Inc., Middleton, Mass.)^TM3550; ebecryl from UBC Radcure, Inc. (UBC Radcure, Smyrna, GA.) of Schmida, Georgia^TM230; jeffamine available from Hunsmy Corporation, Houston, Tex^TMT-5000; available from suweiintel corporation of houston, texas (Solvay interloxinc,houston TX) CAPA 720; and Acclaim from Lyondell chemical Company, Houston, Tex.^TM8200。

In some embodiments, the binder layer 10 may include one or more colorants. In particular embodiments, the binder may include one or more fluorescent pigments. Suitable colorants (e.g., pigments) may be selected from, for example, those listed in the above-referenced '444 and' 844 publications. Regardless of whether the binder layer 10 includes, for example, a colorant or the like, the binder layer 10 will contain reflective particles 179 as previously discussed herein. Reflective particles 179 can be compounded with any suitable type of binder precursor in any suitable manner. In some embodiments, the reflective particles 179 can be dispersed in a vehicle or carrier, which is then compounded into a binder precursor.

The discussion herein relates to articles of the general type shown, for example, in fig. 1 and 5 (including an adhesive layer and in the form of, for example, a transfer article). In some embodiments, transparent microspheres bearing a primary reflective layer (strictly speaking, bearing a reflective layer that will become the primary reflective layer when a suitable reflective particle-loaded binder layer is formed) may be provided in articles that do not include a binder layer. For ease of description, such articles will be referred to as "intermediate" articles. Such an intermediate article will comprise a carrier layer carrying transparent microspheres 21, which transparent microspheres 21 comprise protruding areas 25 provided with a reflective layer on portions 28 thereof. These reflective layers may ultimately become embedded layers of the type previously described, but strictly speaking, these reflective layers will not become embedded layers until the adhesive layer 10 is present. Thus, in this particular type of embodiment, such reflective layers would be equivalently characterized as "isolated" reflective layers, meaning that they cover a portion of, but not the entire area of, the protruding regions 25 of the microspheres. In terms of percent area coverage, angular arc, and the like, the various features of the embedded reflective layer will be understood to apply in a similar manner to the isolated reflective layer in an intermediate article in which the binder layer has not yet been disposed to form the final article. Any such carrier layer 110 as disclosed herein can be disposable, which term broadly encompasses a carrier layer that is removed prior to actual use of the retroreflective article, after which the carrier layer is disposed, recycled, reused, and the like.

Any such intermediate article comprising transparent microspheres having an isolated reflective layer thereon can be further processed to provide a retroreflective article comprising a primary reflective layer and a secondary reflective layer as disclosed herein. That is, a binder layer including reflective particles (and optionally including any desired colorants, pigments, etc.) can be disposed on a microsphere-bearing carrier layer to form a retroreflective article. The intermediate article having any suitable configuration can be shipped to a customer who can configure the adhesive layer thereon to form a customized article, for example, using the methods disclosed herein.

The discussion herein is primarily directed to retroreflective articles in which the regions 24 of the microspheres 21 exposed (i.e., protruding) to the forward direction of the binder 10 are exposed to the ambient atmosphere (e.g., air) in the final retroreflective article in use. In other embodiments, the exposed areas 24 of the microspheres 21 may be covered by and/or reside within a cover layer that is a permanent component of the article 1. Such articles will be referred to as encapsulated lens retroreflective articles. In this case, the transparent microspheres may be selected to include a refractive index that performs appropriately in combination with the refractive index of the cover layer. In various embodiments, in an encapsulated lenticular retroreflective article, the microspheres 21 can include a refractive index (e.g., obtained by the material composition of the microspheres and/or by any kind of surface coating present thereon) of at least 2.0, 2.2, 2.4, 2.6, or 2.8. In some embodiments, the encapsulated lens retroreflective overlay can include a sublayer. In this case, the refractive indices of the microspheres and the sub-layers may be selected in combination.

In some implementations, such a cover layer can be a transparent layer. In other embodiments, the entire or selected areas of the cover layer may be colored (e.g., may comprise one or more colorants) as desired. In some embodiments, the cover layer may take the form of a pre-existing film or sheet disposed (e.g., laminated) to at least selected areas of the front side of the article 1. In other embodiments, the cover layer may be obtained by printing, coating, or otherwise depositing a cover layer precursor onto at least selected areas of the front side of the article 1, and then converting the precursor into the cover layer.

As previously described herein, in some implementations, the color layer 40 can perform wavelength-selective absorption of electromagnetic radiation at least some location within a range including visible light, infrared radiation, and ultraviolet radiation by using a colorant disposed in the color layer. The term colorant broadly encompasses pigments and dyes. Conventionally, a pigment is considered a colorant that is generally insoluble in the material in which it is present, and a dye is considered a colorant that is generally soluble in the material in which it is present. However, it may not always be a clear line distinction as to whether a colorant behaves as a pigment or dye when dispersed into a particular material. Thus, the term colorant encompasses any such material regardless of whether it is considered a dye or pigment in a particular environment. Suitable colorants are described and discussed in detail in the aforementioned U.S. provisional patent application 62/675020.

The transparent microspheres 21 used in any of the articles disclosed herein may be of any suitable type. The term "transparent" is generally used to refer to a body (e.g., glass microspheres) or substrate that transmits at least 50% of electromagnetic radiation at a selected wavelength or within a selected range of wavelengths. In some embodiments, the transparent microspheres can transmit at least 75% of light in the visible spectrum (e.g., about 400nm to about 700 nm); in some embodiments, at least about 80%; in some embodiments, at least about 85%; in some embodiments, at least about 90%; and in some embodiments, at least about 95%. In some embodiments, the transparent microspheres may transmit at least 50% of the radiation at a selected wavelength (or range) in the near infrared spectrum (e.g., 700nm to about 1400 nm). In various embodiments, the transparent microspheres may be made of, for example, inorganic glass, and/or may have a refractive index of, for example, 1.7 to 2.0. (As previously mentioned, the transparent microspheres may be selected to have a higher refractive index as desired in an encapsulated lens arrangement.) in one embodiment, the transparent microspheres may have an average diameter of at least 20 microns, 30 microns, 40 microns, 50 microns, 60 microns, 70 microns, or 80 microns. In further embodiments, the transparent microspheres may have an average diameter of up to 200 microns, 180 microns, 160 microns, 140 microns, 120 microns, 100 microns, 80 microns, or 60 microns. The majority (e.g., at least 90% by number) of the microspheres may be at least substantially spherical, or substantially spherical in shape. However, it should be understood that microspheres produced in any real, large-scale process may include a small amount of microspheres that exhibit slight deviations in shape or irregularities. Thus, the use of the term "microspheres" does not require that the shape of these articles must be, for example, perfect or exactly spherical.

U.S. patent application publications 2017/0276844 and 2017/0293056, which are incorporated herein by reference in their entirety, discuss compositions based on, for example, the coefficient of retroreflectivity (R)_A) A method of characterizing retroreflectivity. In various embodiments, at least selected areas of a retroreflective article as disclosed herein can exhibit a coefficient of retroreflectivity that is at least 50 candela, 100 candela, 200 candela, 250 candela, 350 candela, or 450 candela per lux per square meter, measured according to the procedures outlined in these publications (at 0.2 degree observation angle and 5 degree entrance angle). In some embodiments, R is measured at a "head-on" angle of incidence (e.g., 5 degrees)_AMay be the highest. In other embodiments, R is measured at a "glancing" angle (e.g., 50 degrees, or even 88.76 degrees)_AMay be the highest.

In various embodiments, the retroreflective articles disclosed herein can meet ANSI/ISEA 107-: 2013. In many embodiments, the retroreflective articles disclosed herein can exhibit satisfactory or excellent wash durability. Such wash durability may manifest as a high R after a number of (e.g., 25) wash cycles conducted according to the method of ISO 63302A_ARetention ratio (R after washing)_AAnd R before washing_AThe ratio therebetween) as outlined in U.S. patent application publication 2017/0276844. In various embodiments, the retroreflective articles disclosed herein can exhibit at least 30%, 50%, or 75% R after 25 such wash cycles_APercentage of retention. In various embodiments, retroreflective articles as disclosed herein can be knottedAnd an initial R of at least 100 candela or 330 candela per lux per square meter measured as described above_AAny of these retroreflectivity retention properties are exhibited (prior to washing).

The retroreflective articles disclosed herein can be used for any desired purpose. In some embodiments, retroreflective articles as disclosed herein can be configured for use in or with systems that perform, for example, machine vision, remote sensing, surveillance, and the like. Such machine vision systems may rely on, for example, one or more visible and/or near Infrared (IR) image acquisition systems (e.g., cameras) and/or radiation or illumination sources, as well as any other hardware and software required to operate the system. Accordingly, in some embodiments, a retroreflective article as disclosed herein (whether or not it is mounted on a substrate) can be, or work in conjunction with, a component of a machine vision system of any desired type and configuration. Such retroreflective articles can, for example, be configured to be optically interrogated (whether by a visual wavelength or near-infrared camera, e.g., at distances up to several meters, or even up to several hundred meters) regardless of ambient light conditions. Accordingly, in various embodiments, such retroreflective articles can include retroreflective elements that are configured to collectively exhibit any suitable image, code, pattern, or the like that allows information carried by the article to be retrieved by a machine vision system. Exemplary machine vision systems, the manner in which retroreflective articles can be configured for use in such systems, and the manner in which retroreflective articles can be characterized with particular regard to whether they are suitable for such systems are disclosed in U.S. provisional patent application 62/536654, which is incorporated by reference herein in its entirety.

In some embodiments, primary reflective layer 30, color layer 40, and/or overlay layer (e.g., in particular embodiments where the article is an encapsulated-lens retroreflective article) can be disposed in various macroscopic regions of the retroreflective article, rather than collectively occupying the entire article. Such an arrangement may allow images to be visible in retroreflected light (whether such images are highlighted by increased retroreflectivity and/or by enhanced color). In some implementations, such images can be achieved, for example, by performing patterned deposition of a reflective layer. As previously described herein, in various embodiments, retroreflective articles as disclosed herein can be configured to exhibit an image when viewed in retroreflected light, to exhibit an image when viewed in ambient light, or both. If both are present, the image may be substantially the same when viewed in ambient light as when viewed in retroreflected light (e.g., the article may convey the same information in both cases); or the images may be different (e.g., such that different information is conveyed in the ambient light and the retroreflected light).

Various components of retroreflective articles (e.g., transparent microspheres, binder layers, reflective layers, etc.), methods of making such components, and methods of incorporating such components in retroreflective articles in various arrangements are described, for example, in U.S. patent application publications 2017/0131444, 2017/0276844, and 2017/0293056, and U.S. provisional patent application 62/578343, all of which are incorporated by reference herein in their entirety.

It should be understood that retroreflective elements including the primary and secondary reflective layers disclosed herein can be used in any retroreflective article of any suitable design and in any suitable application. In particular, it is noted that the presence of retroreflective elements that include transparent microspheres (along with one or more colored layers, reflective layers, etc.) does not preclude the presence of other retroreflective elements (e.g., so-called cube-corner retroreflectors) that do not include transparent microspheres somewhere in the article.

Although the discussion herein is primarily directed to the use of the retroreflective articles described herein with apparel and similar articles, it should be understood that these retroreflective articles may find use in any application, such as mounted to or present on or near any suitable article or entity. Thus, for example, retroreflective articles as disclosed herein can be used in pavement marking tapes, pavement markings, vehicle markings or signs (e.g., license plates), or generally in any kind of reflective sheeting. In various embodiments, such articles and sheets comprising such articles may present information (e.g., indicia), may provide an aesthetic appearance, or may provide a combination of both purposes.

List of exemplary embodiments

Embodiment 1 is a retroreflective article comprising: a binder layer containing reflective particles; and a plurality of retroreflective elements spaced apart across the length and width of the front side of the binder layer, each retroreflective element comprising transparent microspheres partially embedded in the binder layer so as to exhibit an embedded surface area of the transparent microspheres; wherein the retroreflective article is configured such that at least some of the retroreflective elements comprise a primary reflective layer embedded between the transparent microspheres and the binder layer and covering less than the entire embedded surface area of the transparent microspheres with a portion of the embedded surface area of the transparent microspheres, and wherein the retroreflective article is configured such that a portion of the binder layer containing reflective particles adjacent to a portion of the embedded surface area of the transparent microspheres not covered by the primary reflective layer provides a secondary reflective layer of retroreflective elements; and wherein the primary reflective layer is a non-uniform primary reflective layer configured such that the percent area coverage of the embedded surface region of the transparent microspheres by the primary reflective layer exhibits a coefficient of variation greater than 0.05.

Embodiment 2 is the retroreflective article of embodiment 1, wherein the primary reflective layer is a non-uniform primary reflective layer configured such that the percent area coverage of the embedded surface region of the transparent microspheres by the primary reflective layer exhibits a coefficient of variation of greater than 0.10.

Embodiment 3 is the retroreflective article of any of embodiments 1-2, wherein at least some of the primary reflective layers of the retroreflective article are partially reflective layers.

Embodiment 4 is the retroreflective article of any of embodiments 1-3, wherein the retroreflective article is configured such that at least some of the primary reflective layers each cover less than 60% of the embedded surface area of the transparent microspheres.

Embodiment 5 is the retroreflective article of any of embodiments 1-4, wherein the retroreflective article is configured such that at least some of the primary reflective layers each cover less than 25% of the total surface area of the transparent microspheres of the embedded surface area of the transparent microspheres.

Embodiment 6 is the retroreflective article of any of embodiments 1-5, wherein at least some of the primary reflective layers each occupy, on average, an angular arc that is greater than 5 degrees up to 50 degrees.

Embodiment 7 is the retroreflective article of any of embodiments 1-6, wherein the retroreflective article is configured to include at least some transparent microspheres that do not include the primary reflective layer, and wherein the transparent microspheres that include the primary reflective layer comprise at least 5% up to 95% of the total number of transparent microspheres of the retroreflective article.

Embodiment 8 is the retroreflective article of any of embodiments 1-7, wherein at least some of the retroreflective elements include an intervening layer, at least a portion of which is disposed between the transparent microspheres and the binder layer such that the primary reflective layer is positioned between the intervening layer and the binder layer.

Embodiment 9 is the retroreflective article of any of embodiments 1-8, wherein at least some of the primary reflective layers are partially laminated reflective layers.

Embodiment 10 is the retroreflective article of any of embodiments 1-9, wherein the binder layer includes a colorant.

Embodiment 11 is the retroreflective article of embodiment 10, wherein the colorant comprises a fluorescent pigment.

Embodiment 12 is the retroreflective article of any of embodiments 1-11, wherein at least some of the primary reflective layers include a metallic reflective layer.

Embodiment 13 is the retroreflective article of any of embodiments 1-12, wherein at least some of the primary reflective layers include a reflective layer that is a dielectric reflective layer that includes alternating high refractive index sublayers and low refractive index sublayers.

Embodiment 14 is the retroreflective article of any of embodiments 1-13, wherein at least some of the reflective particles of the binder layer are pearlescent reflective particles.

Embodiment 15 is the retroreflective article of any of embodiments 1-14, wherein the binder layer contains reflective particles loaded with 0.5 wt% reflective particles to 7.5 wt% reflective particles on a dry weight basis.

Embodiment 16 is the retroreflective article of any of embodiments 1-15, wherein the binder layer contains reflective particles that are platy particles, the reflective particles exhibiting, on average, a ratio of thickness to length that is less than 0.1, and a ratio of thickness to width that is less than 0.1.

Embodiment 17 is the retroreflective article of any of embodiments 1-16, wherein the binder layer includes less than 7.0 wt% pearlescent reflective particles.

Embodiment 18 is the retroreflective article of any of embodiments 1-17, wherein the retroreflective article is configured such that at least some of the primary reflective layers each cover less than 40% of the embedded surface area of the transparent microspheres.

Embodiment 19 is the retroreflective article of any of embodiments 1-18, wherein the retroreflective article is configured such that at least some of the primary reflective layers each cover less than 20% of the embedded surface area of the transparent microspheres.

Embodiment 20 is the retroreflective article of any of embodiments 1-19, wherein the retroreflective article is configured to include at least some transparent microspheres that do not include the primary reflective layer disposed thereon, and wherein the transparent microspheres that include the primary reflective layer comprise at least 5% up to 80% of the total number of transparent microspheres of the retroreflective article.

Embodiment 21 is the retroreflective article of any of embodiments 1-20, wherein the retroreflective article is configured to include at least some transparent microspheres that do not include the primary reflective layer disposed thereon, and wherein the transparent microspheres that include the primary reflective layer comprise at least 5% up to 60% of the total number of transparent microspheres of the retroreflective article.

Embodiment 22 is the retroreflective article of any of embodiments 1-21, wherein the primary reflective layer is a non-uniform reflective layer configured such that the percent area coverage of the embedded surface region of the transparent microspheres by the primary reflective layer exhibits a coefficient of variation of greater than 0.20.

Embodiment 23 is the retroreflective article of any of embodiments 1-22, wherein at least 50% of the retroreflective elements each include a primary reflective layer.

Embodiment 24 is the retroreflective article of any of embodiments 1-22, wherein at least 80% of the retroreflective elements each include a primary reflective layer.

Embodiment 25 is a transfer article comprising the retroreflective article of any of embodiments 1-24 and a disposable support layer on which the retroreflective article is removably disposed so that at least some of the transparent microspheres are in contact with the support layer.

Embodiment 26 is a substrate comprising the retroreflective article of any of embodiments 1-24, wherein the binder layer of the retroreflective article is coupled to the substrate, wherein at least some of the retroreflective elements of the retroreflective article face away from the substrate.

Embodiment 27 is the substrate of embodiment 26, wherein the substrate is a fabric of a garment.

Embodiment 28 is the substrate of embodiment 26, wherein the substrate is a support layer that supports the retroreflective article and is configured to be coupled to a fabric of a garment.

Embodiment 29 is a method of making a retroreflective article comprising a plurality of retroreflective elements, at least some of the retroreflective elements comprising a primary reflective layer and a secondary reflective layer, the method comprising: disposing a primary reflective layer or a reflective layer precursor onto a portion of the protruding regions of at least some of the transparent microspheres carried by and partially embedded in a carrier layer; then, if a reflective layer precursor is present, converting the reflective layer precursor into a primary reflective layer; then, providing a binder precursor containing reflective particles on the support layer and on the protruding regions of the transparent microspheres; the binder precursor is then cured to form a retroreflective article that includes a binder layer loaded with reflective particles, and wherein at least some of the retroreflective elements each include a primary reflective layer embedded between the transparent microspheres and the binder layer and covering less than the entire embedded surface area of the transparent microspheres, and further include a secondary reflective layer provided by portions of the binder layer containing reflective particles adjacent to portions of the embedded surface area of the transparent microspheres not covered by the primary reflective layer.

Embodiment 30 is the method of embodiment 29, wherein the step of disposing a reflective layer or a reflective layer precursor onto a portion of the overhanging region of at least some of the transparent microspheres carried by and partially embedded in a carrier layer comprises partially laminating a pre-fabricated reflective layer onto a portion of the overhanging region of the transparent microspheres.

Embodiment 31 is the retroreflective article of any of embodiments 1-24 made by the method of any of embodiments 29-30.

Examples

Material

Test method

Retroreflectivity measurement

The retroreflective performance of the article was evaluated by measuring the coefficient of retroreflectivity using a RoadVista 933 retroreflector (RoadVista, San Diego, CA).

Coefficient of retroreflectivity (R)_A) As described in U.S. patent 3,700,305:

R_A＝E₁*d²/E₂*A

R_Aintensity of retroreflection

E₁Intensity of light incident on the receiver

E₂Incident ray perpendicular to the sample positionThe illuminance of the plane of (1) and (E)₁Measured in the same units

d-distance from sample to projector

A ═ area of test surface

The retroreflectivity measurement Test procedure followed the Test standards described in "ASTM E810-03(2013) -Standard Test Method for characterizing Retroreflective Sheeting using the Coplanar Geometry". Retroreflective units in cd/lux/m²And (6) reporting. Such as ANSI/ISEA 107-: 2013 requires that the coefficient of retroreflectivity performance value be minimal at a particular combination of entrance angle and observation angle. The angle of incidence is defined as the angle between the illumination axis and the retroreflector axis. The viewing angle is defined as the angle between the illumination axis and the viewing axis.

Color measurement

The color of the retroreflective article can be described in terms of a luminance-chrominance color space (Yxy), where Y is the luminance of the color and x and Y are the chromaticity coordinates. These values are related to the CIE XYZ color space (CIE 1931):

x＝X/(X+Y+Z)

y＝Y/(X+Y+Z)

the advantages of using the Yxy color space are: chromaticity can be plotted, commonly referred to as the CIE x-y chromaticity diagram. This color representation/nomenclature is used in high visibility security administration standards, such as ANSI/isaa 107-: 2013. the color measurement procedure followed the procedure outlined in ASTM E308-90, with the following operating parameters:

standard lighting body: d65 daylight illuminator

Standard observer: CIE (International Commission on illumination) 19312 °

Wavelength interval: 400 nm-700 nm at intervals of 10 nm

Incident light: 0 DEG on the sample plane

And (4) observation: passing 16 fibre-optic receptor stations at 45 ° through a circle

Observation area: one inch

Port size: one inch

Working examples

Working examples describe the production of retroreflective articles that include an embedded primary reflective layer; and using a binder layer loaded with reflective particles to provide a secondary reflective layer. The following examples use a partial lamination process to provide the primary reflective layer and use five main steps:

A. making temporary bead carriers

B. Disposing a bonding layer on a temporary bead carrier

C. Making a transfer stack comprising a reflective layer

D. Transfer of reflective layer to temporary bead support

E. Forming a binder layer on a temporary bead carrier

A. Making temporary bead carriers

In the examples, glass microspheres (beads) were partially and temporarily embedded in a carrier sheet. The carrier sheet comprises a paper juxtaposed with a polyethylene layer about 25 to 50 microns thick. The carrier sheet was heated to 220 ° F (104 ℃) in a convection oven and then the microspheres were poured onto the polyethylene side of the sheet and allowed to stand for 60 seconds. The sheet was removed from the oven and allowed to cool to room temperature. Excess beads were poured off the sheet and the sheet was placed in an oven at 320 ° F (160 ℃) for 60 seconds. The sheet was removed from the oven and allowed to cool. Partially embedding the microspheres in the polyethylene layer allows more than 50% of the microspheres to protrude.

B. Disposing a bonding layer on a temporary bead carrier

A solution containing 6.18 parts of resin 1, 0.13 parts of SILANE-1, 0.5 parts of ICN 1, and 33.41 parts of MEK was mixed into a MAX 40 x speed mixer cup and further mixed in a DAC150.1FVZ-K x speed mixer (FlackTek Inc, Landrum, south carolina) at 2400rpm for 60 seconds. The solution was coated onto the temporary bead carrier using a notch bar coater with a gap of 0.002 inches (0.0510 mm). The sample was then dried at 150 ° F (65.5 ℃) for 3 minutes and cured at 200 ° F (93.3 ℃) for an additional 4 minutes. This results in a polymer-coated temporary bead carrier that includes microspheres whose protruding portions (as well as the exposed surface of the bead carrier) have been coated with an intervening layer of organic polymeric material that serves as a bonding layer to which a reflective layer may subsequently be bonded.

C. Making a transfer stack comprising a reflective layer

The transfer stack was made on a roll-to-roll vacuum coater similar to the coater described in U.S. patent application 20100316852, with the addition of a second evaporator and curing system located between the plasma pretreatment station and the first sputtering system, and using an evaporator as described in U.S. patent 8658248.

The coater was twisted together with a support substrate comprising a release layer in the form of an infinite length roll of heat seal film-1 (aluminized BOPP) 0.001 inch (0.0254mm) thick, 14 inch (356mm) wide. The aluminized (release) side of the substrate was coated with an organic selective bonding layer (acrylate-1) using a web speed of 9.8 meters/minute and the back of the film was held in contact with a coating drum cooled to-10 ℃. A layer of acrylate-1 was deposited on top of the aluminized side of the heat seal film-1 in-line. The acrylate layer was applied by ultrasonic atomization and flash evaporation to give a coating width of 12.5 inches (318 mm). Controlling the flow rate of the material to target a 90nm layer thickness; the temperature of the evaporator was 260 ℃. Once condensed onto the aluminum layer, the monomer coating was cured immediately with an electron beam curing gun operating at 7.0kV and 10.0 mA. The thickness of the organic selective bonding layer thus formed was estimated to be 90 nm.

On top of this organic selective bonding layer, a reflective layer of Ag metal was applied using a cathode Ag target (ACI alloy of San Jose, CA). The Ag reflective layer was deposited by a conventional DC sputtering process with Ar gas, operating at a power of 3kW and at a line speed of 9.8 meters/min to 3 passes per pass to deposit a 90nm thick Ag layer.

On the Ag reflective layer, an embrittlement layer comprising an inorganic oxide (aluminum silicon alumina) layer is applied. The oxide was laid down by an AC reactive sputter deposition process using a 40kHz AC power supply. The cathode has a Si (90%)/Al (10%) rotating target deposited in an oxygen-containing atmosphere, available from soras advanced coatings US of bisford, maine (of bididheford (ME)). During sputtering, the voltage at the cathode is controlled by a feedback control loop that monitors the voltage and controls the oxygen flow rate so that the voltage remains high without collapse of the target voltage. The system was operated at 16kW power and 32fpm to deposit a 6nm thick layer of silicon aluminum oxide onto the Ag layer.

Thus, these operations provide a transfer stack that includes a peelable support assembly (aluminized BOPP) and a reflective layer disposed on the peelable support assembly. The reflective layer is a multilayer structure comprising a selectively bonding organic layer, an Ag reflective layer on top of the selectively bonding layer, and an oxide embrittlement layer on top of the Ag reflective layer. The reflective layer is disposed on the releasable support assembly such that a major surface of the selectively bonded organic layer of the reflective layer is in contact with a major surface of the aluminum release layer of the releasable support assembly such that a selective releasable interface exists therebetween. The transfer stack may be stored (e.g., in roll form) until ready to continue the transfer.

D. Transfer of reflective layer to temporary bead support (polymer coated)

Contacting and pressing the transfer stack of step C) against the polymer-coated temporary bead carrier of step B in a room temperature nip at a layer pressure of 500 pounds per linear inch (87.5kN/m) at 10fpm (4.2 millimeters per second). The silicon alumina surface of the transfer stack is in contact with the bonding layer of the polymer-coated temporary bead support. The nip comprised a rubber-surfaced roll of approximately 70 shore a bearing the heat-sealable film-1 substrate of the transfer stack and a steel roll bearing the paper side of the polymer-coated bead carrier. The process causes the silicon aluminum oxide layer to bond to the bonding layer present on the protruding surface of the glass microspheres at the location where contact between the two layers occurs. Thus, localized lamination of areas of the reflective layer of the transfer stack to glass microspheres of the polymer-coated temporary bead support is achieved.

After lamination, the heat-seal film-1 (peelable support assembly) was separated from the reflective layer to create a transfer bead carrier. The separation of the releasable support assembly from the reflective layer occurs at the selectively releasable interface between the aluminum surface of the heat seal film-1 and the organic selective bonding layer of the reflective layer. The opposite surface of the organic selective bonding layer remains well bonded to the Ag reflective layer, as does the silicon aluminum oxide embrittled layer.

E. Formation and transfer of reflective particle loaded binder layer

A binder precursor mixture consisting of 59.7 parts resin 1, 10.8 parts resin 2, 6.8 parts pigment 1, 3.7 parts ICN-1, 1.4 parts SILANE-1, 1 part 10% MEK, and 6.8 parts MIBK was mixed into a MAX 40 times speed mixer cup and further mixed in an DAC150.1FVZ-K times speed mixer (Frankel, Landlur, N.C.) at 2400rpm for 60 seconds. Various amounts of reflective pigment 1 (corresponding to 0 wt%, 2 wt%, 5.6 wt%, and 9.1 wt%, respectively, of the total wet formulation weight) were added. The% solids of reflective pigment 1 was about 65%. Thus, for the sample in which reflective pigment 1 was added in an amount of 9.1 wt% of the total wet formulation weight, the dry solids after solvent removal of the reflective pigment accounted for about 7.4 wt% of the total dry solids of the binder layer.

Each binder precursor mixture was coated onto a transfer bead carrier sample using a laboratory notch bar coater set to a wet coating thickness of 8 mils. The coated sample was then dried at 150 ° F for 30 seconds and subsequently cured at 180 ° F (82.2 ℃) for an additional 3 minutes. The resulting samples were then laminated to an aramid fabric comprising a white adhesive layer using a roll laminator operating at about 50psi, 220 ° F (104.4 ℃) and a roll speed of about 0.75 inches/second (19 mm/second).

The resulting article is a transfer article comprising a retroreflective article disposed on a temporary bead support (paper-polyethylene carrier sheet). The temporary bead carrier (with the microspheres and various layers separated from the temporary bead carrier) may then be removed as desired.

Retroreflectivity and color evaluation

The temporary bead carrier was removed from all samples for testing. Both retroreflectivity and color were measured. Using the general method described above, at observation angles (0.2 degrees, 0.33 degrees, 1 degree, 1.5 degrees), incidence angles (5 degrees, 20 degrees, 30 degrees, and 40 degrees), and sample orientations(0 degree and 90 degree rotation) the coefficient of retroreflectivity was measured using a RoadVista type field retroreflectivity reflectometer (UDT instrument (Gamma Scientific, UDT Instruments, San Diego, CA) from Gamma science, San Diego, CA). Coefficient of retroreflectivity (R)_A) Has the unit of cd/lux/m². Color measurements were made using a ColorFlex 45/0 colorimeter from Hunter laboratories (Hunter Lab). Color data is reported in Yxy units, where Y is the color luminance and x and Y represent the chromaticity coefficients (as defined in the CIE Yxy color space chromaticity diagram). Data was collected at the same location on the sample for both retroreflectivity and color.

The results of the retroreflectivity test are shown in table 1, and the results of the color test are shown in table 2. The sample identified as 0.0% reflective pigment 1 is a comparative example.

TABLE 1

TABLE 2

	0.0% of reflective pigment 1	2.0% of reflective pigment 1	5.6% of reflective pigment 1	9.1% of reflective pigment 1
					Y	98.52	99.32	94.47	89.37
x	0.3756	0.3264	0.3706	0.3786
					y	0.5288	0.5289	0.5131	0.511

Those skilled in the art will recognize that table 1 presents a "32-angle" test cell of the type ISO 20471: 2013 (high visibility garment-test method and requirements) and is often used in the evaluation of, for example, safety garments. In table 1, OA is the observation angle, EA is the incidence angle, and the orientation is the orientation of the sample. The measured data were compared to minimum specifications ("Spec") defined for a combined performance high visibility safety garment standard (table 5 in ISO 20471: 2013). It should be understood, however, that not all uses will require retroreflective articles to meet these particular specifications.

The data show that the combination of primary and secondary reflective layers as disclosed herein can produce acceptable or even excellent retroreflective performance under both general "head-on" conditions (e.g., at an entrance angle of 40 degrees) and "off-angle" conditions (e.g., at an entrance angle of 5 degrees). At the same time, good or excellent color was maintained as evidenced by the Y (color luminosity) values presented in table 2. In more detail, as is apparent from table 1, increasing the level of reflective particles in the binder layer when the primary reflective layer is present can significantly increase retroreflective performance at "off-angles" while having a small (e.g., insignificant) effect on retroreflective performance at "on-face" angles. This effect of the secondary reflective layer on enhancing the off-angle retroreflectivity is achieved even if the binder layer contains a large amount of fluorescent pigment.

Examples that do not include the formation of a secondary reflective layer but are used as reference examples, such as those found in, for example, U.S. provisional patent application 62/739,489 (attorney docket No. 80012US003), which is incorporated herein by reference in its entirety, examples 2-1, 2-2-2, 2.3, 2.4, 3.1.1, and 3.1-2, can effectively illustrate further details of various ways in which a primary reflective layer can be made. One of ordinary skill will appreciate that the methods and arrangements of these reference examples can be used in combination with a binder layer comprising reflective particles to produce retroreflective articles comprising a primary reflective layer and a secondary reflective layer in the manner disclosed herein.

The foregoing embodiments have been provided merely for the purpose of clarity of understanding and are not to be construed as unnecessarily limiting. The tests and test results described in the examples are intended to be illustrative rather than predictive, and variations in the testing process may be expected to yield different results. All quantitative values in the examples are to be understood as approximations based on the commonly known tolerances involved in the procedures used.

It will be apparent to those of ordinary skill in the art that the specific exemplary elements, structures, features, details, configurations, etc., disclosed herein can be modified and/or combined in many embodiments. The inventors contemplate that all such variations and combinations are within the scope of the contemplated invention, not just those representative designs selected to serve as exemplary illustrations. Thus, the scope of the present invention should not be limited to the particular illustrative structures described herein, but rather extends at least to the structures described by the language of the claims and the equivalents of those structures. Any elements which are positively recited in the specification as alternatives may be explicitly included in or excluded from the claims in any combination as desired. Any element or combination of elements recited in this specification in an open-ended language (e.g., including and derived from) is considered to be encompassed in a closed-ended language (e.g., consisting of and derived from). While various theories and possible mechanisms may have been discussed herein, such discussion should not be used in any way to limit the subject matter which may be claimed. In the event of any conflict or conflict between a written specification and the disclosure in any document incorporated by reference herein, the written specification shall control.

Claims

1. A retroreflective article comprising:

a binder layer containing reflective particles; and the combination of (a) and (b),

a plurality of retroreflective elements spaced apart across the length and width of the front side of the binder layer, each retroreflective element comprising transparent microspheres partially embedded in the binder layer so as to exhibit an embedded surface area of the transparent microspheres;

wherein the retroreflective article is configured such that at least some of the retroreflective elements include a primary reflective layer embedded between the transparent microspheres and the binder layer and the primary reflective layer covers less than the entire embedded surface area of the transparent microspheres and

wherein the retroreflective article is configured such that a portion of the binder layer containing reflective particles adjacent to a portion of the embedded surface area of the transparent microspheres not covered by the primary reflective layer provides a secondary reflective layer of the retroreflective elements;

and the number of the first and second electrodes,

wherein the primary reflective layer is a non-uniform primary reflective layer configured such that the primary reflective layer exhibits a coefficient of variation of greater than 0.05 in percent area coverage of the embedded surface region of the transparent microspheres.

2. The retroreflective article of claim 1, wherein the primary reflective layer is a non-uniform primary reflective layer configured such that the percent area coverage of the embedded surface region of transparent microspheres by the primary reflective layer exhibits a coefficient of variation of greater than 0.10.

3. The retroreflective article of claim 1, wherein at least some of the primary reflective layers of the retroreflective article are partially reflective layers.

4. The retroreflective article of claim 1, wherein the retroreflective article is configured such that at least some of the primary reflective layers each cover less than 60% of an embedded surface area of transparent microspheres.

5. The retroreflective article of claim 1, wherein the retroreflective article is configured such that at least some of the primary reflective layers each cover less than 25% of the total surface area of the transparent microspheres of the embedded surface area of the transparent microspheres.

6. The retroreflective article of claim 1, wherein at least some of the primary reflective layers each occupy, on average, an angular arc that is greater than 5 degrees up to 50 degrees.

7. The retroreflective article of claim 1, wherein the retroreflective article is configured to include at least some transparent microspheres that do not include a primary reflective layer, and wherein the transparent microspheres that include a primary reflective layer comprise at least 5% up to 95% of the total number of transparent microspheres of the retroreflective article.

8. The retroreflective article of claim 1, wherein at least some of the retroreflective elements include an intervening layer, at least a portion of the intervening layer being disposed between the transparent microspheres and the binder layer such that the primary reflective layer is positioned between the intervening layer and the binder layer.

9. The retroreflective article of claim 1, wherein at least some of the primary reflective layers are partially laminated reflective layers.

10. The retroreflective article of claim 1, wherein the binder layer includes a colorant.

11. The retroreflective article of claim 10, wherein the colorant includes a fluorescent pigment.

12. The retroreflective article of claim 1, wherein at least some of the primary reflective layers include a metallic reflective layer.

13. The retroreflective article of claim 1, wherein at least some of the primary reflective layers include a reflective layer that is a dielectric reflective layer that includes alternating high and low refractive index sublayers.

14. The retroreflective article of claim 1, wherein at least some of the reflective particles of the binder layer are pearlescent reflective particles.

15. The retroreflective article of claim 1, wherein the binder layer contains reflective particles loaded with 0.5 wt% reflective particles to 7.5 wt% reflective particles on a dry weight basis.

16. The retroreflective article of claim 1, wherein the binder layer contains reflective particles that are plate-like particles that, on average, exhibit a ratio of thickness to length that is less than 0.1, and a ratio of thickness to width that is less than 0.1.

17. A transfer article comprising the retroreflective article of claim 1 and a disposable carrier layer on which the retroreflective article is removably disposed with at least some of the transparent microspheres in contact with the carrier layer.

18. A substrate comprising the retroreflective article of claim 1, wherein the binder layer of the retroreflective article is coupled to the substrate with at least some of the retroreflective elements of the retroreflective article facing away from the substrate.

19. The substrate of claim 18, wherein the substrate is a fabric of a garment.

20. The substrate of claim 18, wherein the substrate is a support layer that supports the retroreflective article and is configured to be coupled to a fabric of a garment.

21. A method of making a retroreflective article comprising a plurality of retroreflective elements, at least some of the plurality of retroreflective elements comprising a primary reflective layer and a secondary reflective layer, the method comprising:

disposing a primary reflective layer or a reflective layer precursor onto a portion of the protruding regions of at least some of the transparent microspheres carried by and partially embedded in a carrier layer; then, the user can use the device to perform the operation,

converting the reflective layer precursor, if present, into a primary reflective layer; then, the user can use the device to perform the operation,

providing a binder precursor containing reflective particles on the support layer and on the protruding regions of the transparent microspheres; then, the user can use the device to perform the operation,

curing the binder precursor to form a retroreflective article that includes a binder layer loaded with reflective particles, and wherein at least some of the retroreflective elements each include a primary reflective layer embedded between transparent microspheres and the binder layer and the portion of the embedded surface area of the transparent microspheres covered by the primary reflective layer is less than the entire embedded surface area of the transparent microspheres, and further includes a secondary reflective layer provided by a portion of the binder layer containing reflective particles adjacent to the portion of the embedded surface area of the transparent microspheres not covered by the primary reflective layer.

22. The method of claim 21, wherein the step of disposing a reflective layer or reflective layer precursor onto a portion of the overhanging region of at least some of the transparent microspheres carried by a carrier layer and partially embedded in the carrier layer comprises partially laminating a pre-fabricated reflective layer onto the portion of the overhanging region of the transparent microspheres.